Glutathione synthesis, recycling, and the gamma-glutamyl cycle

Glutathione (GSH, gamma-L-glutamyl-L-cysteinylglycine) is the most abundant cellular thiol and the central small-molecule antioxidant and redox buffer, also serving in detoxification (as GSH conjugates), cysteine storage/transport and leukotriene metabolism. Its metabolism has three linked arms. Synthesis is a two-step, ATP-dependent cytosolic route: glutamate-cysteine ligase (GCL, a heterodimer of the catalytic subunit GCLC and the regulatory modifier subunit GCLM) joins L-glutamate and L-cysteine to gamma-glutamylcysteine (the rate-limiting, feedback-controlled step), and glutathione synthetase (GSS) adds glycine to make GSH. Recycling keeps the pool reduced: glutathione-disulfide reductase (GSR), an FAD/NADPH enzyme, reduces oxidized glutathione (GSSG) back to two GSH, sustaining the high GSH/GSSG ratio. Turnover proceeds through the gamma-glutamyl cycle: the cell-surface ectoenzyme gamma-glutamyltransferase GGT1 initiates extracellular GSH breakdown by transferring/hydrolysing its gamma-glutamyl group (yielding cysteinylglycine plus a gamma-glutamyl-amino acid), gamma-glutamylcyclotransferase (GGCT) converts the gamma-glutamyl-amino acid to 5-oxoproline plus the free amino acid, and 5-oxoprolinase (OPLAH) hydrolyses 5-oxoproline back to glutamate at the expense of ATP, closing the cycle. A parallel intracellular route, the ATF4/stress-induced glutathione-specific gamma-glutamylcyclotransferase CHAC1, degrades cytosolic GSH directly to 5-oxoproline plus cysteinylglycine (promoting apoptosis/ferroptosis on GSH depletion). Inherited defects cause hemolytic anemia (GCLC, GSR), glutathione synthetase deficiency / 5-oxoprolinuria (GSS), glutathionuria (GGT1) and 5-oxoprolinase deficiency (OPLAH). In fungi the cycle is organised differently: the gamma-glutamyl transpeptidase is a vacuolar-membrane enzyme that degrades glutathione stored in the vacuole, no GGCT-type gamma-glutamylcyclotransferase is present, and a cytosolic alternative (DUG) pathway cleaves glutathione with a Dug2-Dug3 glutamine-amidotransferase complex before an M20A-family Cys-Gly dipeptidase (Dug1; human CNDP2) releases cysteine and glycine.

MODULE:glutathione_synthesis_gamma_glutamyl_cycleDRAFTMetabolic Pathwaymodules/glutathione_synthesis_gamma_glutamyl_cycle.yaml
glutathione biosynthetic processGO:0006750 glutathione catabolic processGO:0006751
GO:0006750
glutathione biosynthetic process
GCLC/GCLM and GSS carry out glutathione biosynthesis (GO:0006750).
GO:0006751
glutathione catabolic process
GGT1, GGCT, OPLAH and CHAC1 mediate glutathione catabolism / the gamma-glutamyl cycle (GO:0006751).
file:human/GCLC/GCLC-ai-review.yaml
GCLC gene review (human)
The rate-limiting gamma-glutamylcysteine synthesis step (UniProtKB:P48506, GO:0004357) matches the completed human GCLC review.
file:human/GCLM/GCLM-ai-review.yaml
GCLM gene review (human)
The GCL modifier subunit (UniProtKB:P48507, GO:1990609 + GO:0017109) matches the completed human GCLM review.
file:human/GSS/GSS-ai-review.yaml
GSS gene review (human)
The glutathione synthetase step (UniProtKB:P48637, GO:0004363) matches the completed human GSS review.
file:human/GSR/GSR-ai-review.yaml
GSR gene review (human)
The GSSG->2 GSH recycling step (UniProtKB:P00390, GO:0004362) matches the completed human GSR review.
file:human/GGT1/GGT1-ai-review.yaml
GGT1 gene review (human)
The extracellular gamma-glutamyl transfer step (UniProtKB:P19440, GO:0036374) matches the completed human GGT1 review.
file:human/GGCT/GGCT-ai-review.yaml
GGCT gene review (human)
The gamma-glutamylcyclotransferase step (UniProtKB:O75223, GO:0003839) matches the completed human GGCT review.
file:human/OPLAH/OPLAH-ai-review.yaml
OPLAH gene review (human)
The 5-oxoprolinase (cycle-closing) step (UniProtKB:O14841, GO:0017168) matches the completed human OPLAH review.
file:human/CHAC1/CHAC1-ai-review.yaml
CHAC1 gene review (human)
The intracellular glutathione-degrading step (UniProtKB:Q9BUX1, GO:0061928) matches the completed human CHAC1 review.
YeastPathways:GLUTATHIONESYN-PWY
glutathione biosynthesis (S. cerevisiae, SGD YeastPathways)
GSH1 and GSH2; retained.
YeastPathways:PWYQT-4432
glutathione degradation (S. cerevisiae, SGD YeastPathways)
RXN-6601 (ECM38) and RXN-6622 (DUG1). The frame comment still states that the Cys-Gly dipeptidase gene is unknown, but DUG1 is assigned (PMID:19346245); DUG2/DUG3 are mentioned but not assigned to a reaction.
YeastPathways:PWY3O-114
superpathway of glutathione metabolism (truncated gamma-glutamyl cycle) (S. cerevisiae, SGD YeastPathways)
GSH1, GSH2, ECM38 and DUG1. The comment questions whether yeast has a 5-oxoprolinase; OXP1 is one (PMID:20402795), and GCG1 is a glutathione-specific ChaC enzyme.
PMID:12702279
An overview on glutathione in Saccharomyces versus non-conventional yeasts.
Review of glutathione metabolism in yeasts.
PMID:6143574
Glutathione metabolism in yeast Saccharomyces cerevisiae. Evidence that gamma-glutamyltranspeptidase is a vacuolar enzyme.
Yeast gamma-GT follows vacuolar markers on fractionation.
PMID:11672438
gamma-Glutamyl transpeptidase in the yeast Saccharomyces cerevisiae and its role in the vacuolar transport and metabolism of glutathione.
gamma-GT is bound to the vacuolar membrane and, with a Cys-Gly dipeptidase, hydrolyses vacuolar GSH.
is a glycoprotein that is bound to the vacuolar membrane.
PMID:9202464
An important role for glutathione and gamma-glutamyltranspeptidase in the supply of growth requirements during nitrogen starvation of the yeast Saccharomyces cerevisiae.
Vacuolar GSH and gamma-GT supply amino acids during nitrogen starvation.
PMID:12620619
Utilization of glutathione as an exogenous sulfur source is independent of gamma-glutamyl transpeptidase in the yeast Saccharomyces cerevisiae: evidence for an alternative gluathione degradation pathway.
GSH can be used as a sulfur source without gamma-GT, revealing an alternative degradation route.
PMID:17179087
The alternative pathway of glutathione degradation is mediated by a novel protein complex involving three new genes in Saccharomyces cerevisiae.
DUG1, DUG2 and DUG3 are required for the alternative GSH degradation pathway; the proposed three-protein degradosome was later resolved into a (Dug2p-Dug3p)2 GATase acting upstream of the Dug1p dipeptidase (PMID:22277648).
PMID:22277648
Glutathione degradation by the alternative pathway (DUG pathway) in Saccharomyces cerevisiae is initiated by (Dug2p-Dug3p)2 complex, a novel glutamine amidotransferase (GATase) enzyme acting on glutathione.
(Dug2p-Dug3p)2 cleaves GSH to glutamate and Cys-Gly; Dug1p acts downstream as the Cys-Gly peptidase.
PMID:19346245
Dug1p Is a Cys-Gly peptidase of the gamma-glutamyl cycle of Saccharomyces cerevisiae and represents a novel family of Cys-Gly peptidases.
Dug1p, S. pombe dug1 and human CNDP2 are M20A Cys-Gly dipeptidases.
The human orthologue CNDP2 also displays Cys-Gly peptidase activity
PMID:20402795
OXP1/YKL215c encodes an ATP-dependent 5-oxoprolinase in Saccharomyces cerevisiae: functional characterization, domain structure and identification of actin-like ATP-binding motifs in eukaryotic 5-oxoprolinases.
OXP1 is the yeast ATP-dependent 5-oxoprolinase.
PMID:23070364
Mammalian proapoptotic factor ChaC1 and its homologues function as γ-glutamyl cyclotransferases acting specifically on glutathione.
ChaC-family enzymes, conserved across phyla, degrade glutathione to 5-oxoproline and Cys-Gly.
PMID:8843443
Yeast glutathione reductase is required for protection against oxidative stress and is a target gene for yAP-1 transcriptional regulation.
GLR1 encodes yeast glutathione reductase.
12Nodes
9Parts
1Variant Sets
2Variants
12Annotons
12Connections

Derived QC

Recommended-field compliance

100.0% recommended fields populated

All recommended fields populated.

Module deep research

✗ none found

No MODULE:glutathione_synthesis_gamma_glutamyl_cycle deep-research report alongside the module YAML.

Leaf nodes lacking representative members

✓ every leaf node grounds to a representative protein.

Template conformance

✓ every declared conforms_to bundle matches its template motif.

Reaction chaining (advisory)

✓ every PRECEDES step chains, or its break is acknowledged via chaining_status.

  • glutamate_cysteine_ligation → glutathione_synthesis [NOT_CHECKED]
    gamma-Glutamylcysteine links the steps; no CoA carrier is involved.

Function consistency and core coverage

23 gene-function check(s) reflected in core functions · 0 conflict(s) · 3 evidence or coverage gap(s) (36 comparison(s))

Retained noncore functions are reported separately; they do not require promotion to core functions. Support from representative genes does not establish conservation across the whole family. Missing reviews or identifiers leave a claim unverified.

AnnotonParticipantFunctionAssessment
gclc_activity GCLC (human)
UniProtKB:P48506
Family Representative 		glutamate-cysteine ligase activity
GO:0004357 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
gclc_activity GSH1 (Saccharomyces cerevisiae)
UniProtKB:P32477
Family Representative 		glutamate-cysteine ligase activity
GO:0004357 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
gclc_activity gcs1 (Schizosaccharomyces pombe)
UniProtKB:Q09768
Family Representative 		glutamate-cysteine ligase activity
GO:0004357 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
gss_activity GSS (human)
UniProtKB:P48637
Family Representative 		glutathione synthase activity
GO:0004363 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
gss_activity GSH2 (Saccharomyces cerevisiae)
UniProtKB:Q08220
Family Representative 		glutathione synthase activity
GO:0004363 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
gss_activity gsa1 (Schizosaccharomyces pombe)
UniProtKB:P35669
Family Representative 		glutathione synthase activity
GO:0004363 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
gsr_activity GSR (human)
UniProtKB:P00390
Family Representative 		glutathione-disulfide reductase (NADPH) activity
GO:0004362 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
gsr_activity GLR1 (Saccharomyces cerevisiae)
UniProtKB:P41921
Family Representative 		glutathione-disulfide reductase (NADPH) activity
GO:0004362 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
gsr_activity pgr1 (Schizosaccharomyces pombe)
UniProtKB:P78965
Family Representative 		glutathione-disulfide reductase (NADPH) activity
GO:0004362 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
ggt1_activity GGT1 (human)
UniProtKB:P19440
Family Representative 		glutathione gamma-glutamate hydrolase activity
GO:0036374 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
fungal_vacuolar_ggt_activity ECM38/CIS2 (Saccharomyces cerevisiae)
UniProtKB:Q05902
Family Representative 		glutathione gamma-glutamate hydrolase activity
GO:0036374 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
fungal_vacuolar_ggt_activity ggt1 (Schizosaccharomyces pombe)
UniProtKB:Q9US04
Family Representative 		glutathione gamma-glutamate hydrolase activity
GO:0036374 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
fungal_vacuolar_ggt_activity ggt2 (Schizosaccharomyces pombe)
UniProtKB:O14194
Family Representative 		glutathione gamma-glutamate hydrolase activity
GO:0036374 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
ggct_activity GGCT (human)
UniProtKB:O75223
Family Representative 		gamma-glutamylcyclotransferase activity
GO:0003839 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
chac1_activity CHAC1 (human)
UniProtKB:Q9BUX1
Family Representative 		glutathione specific gamma-glutamylcyclotransferase activity
GO:0061928 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
chac1_activity GCG1 (Saccharomyces cerevisiae)
UniProtKB:P32656
Family Representative 		glutathione specific gamma-glutamylcyclotransferase activity
GO:0061928 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
chac1_activity ggg1 (Schizosaccharomyces pombe)
UniProtKB:P87305
Family Representative 		glutathione specific gamma-glutamylcyclotransferase activity
GO:0061928 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
oplah_activity OPLAH (human)
UniProtKB:O14841
Family Representative 		5-oxoprolinase (ATP-hydrolyzing) activity
GO:0017168 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
oplah_activity OXP1 (Saccharomyces cerevisiae)
UniProtKB:P28273
Family Representative 		5-oxoprolinase (ATP-hydrolyzing) activity
GO:0017168 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
oplah_activity oxp1 (Schizosaccharomyces pombe)
UniProtKB:Q10094
Family Representative 		5-oxoprolinase (ATP-hydrolyzing) activity
GO:0017168 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
oplah_activity oxp2 (Schizosaccharomyces pombe)
UniProtKB:Q10093
Family Representative 		5-oxoprolinase (ATP-hydrolyzing) activity
GO:0017168 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
dug1_cysgly_dipeptidase_activity DUG1 (Saccharomyces cerevisiae)
UniProtKB:P43616
Family Representative 		metallodipeptidase activity
GO:0070573 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
dug1_cysgly_dipeptidase_activity dug1 (Schizosaccharomyces pombe)
UniProtKB:Q9P6I2
Family Representative 		metallodipeptidase activity
GO:0070573 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
dug1_cysgly_dipeptidase_activity CNDP2 (human)
UniProtKB:Q96KP4
Family Representative 		metallodipeptidase activity
GO:0070573 		Review Missing
No ai-review exists for this protein; its function and core-function coverage cannot yet be checked.
dug3_gatase_activity DUG3 (Saccharomyces cerevisiae)
UniProtKB:P53871
Gene 		glutathione gamma-glutamate hydrolase activity
GO:0036374 		Annotation Supported
A retained annotation or curated replacement supports this function, but core_functions does not yet reflect it.
gclc_activity GCLC / glutamate-cysteine ligase catalytic family
PANTHER:PTHR11164
Family 		glutamate-cysteine ligase activity
GO:0004357 		Family Supported
Family review supports GO:0004357 FAMILY_WIDE. Asserted by glutathione_synthesis_gamma_glutamyl_cycle; accepted by GSH1, gcs1 and GCLC.
gss_activity GSS / glutathione synthetase family
PANTHER:PTHR11130
Family 		glutathione synthase activity
GO:0004363 		Family Supported
Family review supports GO:0004363 FAMILY_WIDE. Asserted by glutathione_synthesis_gamma_glutamyl_cycle; accepted by GSH2, gsa1, GSS and rat Gss.
gsr_activity GSR / glutathione reductase (pyridine-nucleotide-disulfide oxidoreductase) family
PANTHER:PTHR42737:SF2
Family 		glutathione-disulfide reductase (NADPH) activity
GO:0004362 		Family Supported
Family review supports GO:0004362 for PANTHER:PTHR42737:SF2. GR subfamilies; glutathione_thioredoxin_redox_systems and glutathione_synthesis_gamma_glutamyl_cycle select the base family, which also takes in the TrxRs.
gsr_activity GSR / glutathione reductase (pyridine-nucleotide-disulfide oxidoreductase) family
PANTHER:PTHR42737:SF5
Family 		glutathione-disulfide reductase (NADPH) activity
GO:0004362 		Family Supported
Family review supports GO:0004362 for PANTHER:PTHR42737:SF5. GR subfamilies; glutathione_thioredoxin_redox_systems and glutathione_synthesis_gamma_glutamyl_cycle select the base family, which also takes in the TrxRs.
gsr_activity GSR / glutathione reductase (pyridine-nucleotide-disulfide oxidoreductase) family
PANTHER:PTHR42737:SF9
Family 		glutathione-disulfide reductase (NADPH) activity
GO:0004362 		Family Supported
Family review supports GO:0004362 for PANTHER:PTHR42737:SF9. GR subfamilies; glutathione_thioredoxin_redox_systems and glutathione_synthesis_gamma_glutamyl_cycle select the base family, which also takes in the TrxRs.
ggt1_activity GGT / gamma-glutamyltransferase (Ntn-hydrolase) family
PANTHER:PTHR11686
Family 		glutathione gamma-glutamate hydrolase activity
GO:0036374 		Family Supported
Family review supports GO:0036374 FAMILY_WIDE. Asserted by glutathione_synthesis_gamma_glutamyl_cycle; accepted by GGT1, ECM38, ggt1 and ggt2.
fungal_vacuolar_ggt_activity GGT / gamma-glutamyltransferase (Ntn-hydrolase) family
PANTHER:PTHR11686
Family 		glutathione gamma-glutamate hydrolase activity
GO:0036374 		Family Supported
Family review supports GO:0036374 FAMILY_WIDE. Asserted by glutathione_synthesis_gamma_glutamyl_cycle; accepted by GGT1, ECM38, ggt1 and ggt2.
ggct_activity GGCT / gamma-glutamylcyclotransferase family
PANTHER:PTHR12935
Family 		gamma-glutamylcyclotransferase activity
GO:0003839 		Family Supported
Family review supports GO:0003839 FAMILY_WIDE. Asserted by glutathione_synthesis_gamma_glutamyl_cycle; accepted by human GGCT.
chac1_activity CHAC / glutathione-specific gamma-glutamylcyclotransferase family
PANTHER:PTHR12192
Family 		glutathione specific gamma-glutamylcyclotransferase activity
GO:0061928 		Family Supported
Family review supports GO:0061928 FAMILY_WIDE. Asserted by glutathione_synthesis_gamma_glutamyl_cycle; accepted by GCG1, ggg1 and CHAC1.
oplah_activity OPLAH / 5-oxoprolinase family
PANTHER:PTHR11365:SF2
Family 		5-oxoprolinase (ATP-hydrolyzing) activity
GO:0017168 		Family Supported
Family review supports GO:0017168 for PANTHER:PTHR11365:SF2. SF2; glutathione_synthesis_gamma_glutamyl_cycle selects the base family, which also takes in the bacterial SF23 proteins.
dug1_cysgly_dipeptidase_activity M20A Cys-Gly dipeptidase (DUG1/CNDP2) clade
Family 		metallodipeptidase activity
GO:0070573 		Family Id Missing
The family has no identifier linking it to a curated family review.

Gene-review completeness (27/28 grounded genes reviewed)

26 complete review(s) · 11 with deep research · 1 missing review · 16 reviewed but lacking deep research

Gene Review Complete Deep research
CHAC1 Q9BUX1 ✓ ✓ ✗
DUG1 P43616 ✓ ✓ ✓
dug1 Q9P6I2 ✓ ✓ ✗
DUG2 P38149 ✓ 25/26 ✓
DUG3 P53871 ✓ ✓ ✓
ECM38 Q05902 ✓ ✓ ✓
GCG1 P32656 ✓ ✓ ✓
GCLC P48506 ✓ ✓ ✓
GCLM P48507 ✓ ✓ ✗
gcs1 Q09768 ✓ ✓ ✗
gcs2 O94246 ✓ ✓ ✗
GGCT O75223 ✓ ✓ ✗
ggg1 P87305 ✓ ✓ ✗
GGT1 P19440 ✓ ✓ ✗
ggt1 Q9US04 ✓ ✓ ✗
ggt2 O14194 ✓ ✓ ✗
GLR1 P41921 ✓ ✓ ✓
gsa1 P35669 ✓ ✓ ✗
GSH1 P32477 ✓ ✓ ✓
GSH2 Q08220 ✓ ✓ ✓
GSR P00390 ✓ ✓ ✗
GSS P48637 ✓ ✓ ✓
OPLAH O14841 ✓ ✓ ✗
OXP1 P28273 ✓ ✓ ✓
oxp1 Q10094 ✓ ✓ ✗
oxp2 Q10093 ✓ ✓ ✗
pgr1 P78965 ✓ ✓ ✗
CNDP2 (human) Q96KP4 ✗ — —

Details

Context
eukaryotesNCBITaxon:2759
cytosolGO:0005829 plasma membraneGO:0005886 fungal-type vacuole membraneGO:0000329
Glutathione synthesis, recycling, and the gamma-glutamyl cycleMetabolic Pathwayglutathione_synthesis_gamma_glutamyl_cycle
glutathione biosynthetic processGO:0006750 glutathione catabolic processGO:0006751
Context
eukaryotesNCBITaxon:2759
cytosolGO:0005829 plasma membraneGO:0005886 fungal-type vacuole membraneGO:0000329

Glutathione synthesis (GO:0006750), recycling and the gamma-glutamyl cycle (GO:0006751), grounded to nine completed human gene reviews (GCLC and GSS were reviewed/merged earlier). SYNTHESIS (cytosol): GCL = GCLC (P48506 PTHR11164, GO:0004357 catalytic, rate-limiting, GSH-feedback-inhibited) + GCLM (P48507 PTHR13295, GO:1990609 modifier, in_complex GO:0017109 — non-catalytic, lowers Km/raises feedback Ki) -> GSS (P48637 PTHR11130, GO:0004363 adds glycine -> GSH). RECYCLING: GSR (P00390 PTHR42737, GO:0004362 FAD/NADPH, GSSG->2 GSH). GAMMA-GLUTAMYL CYCLE (turnover): GGT1 (P19440 PTHR11686, GO:0036374 — cell-surface Ntn-hydrolase; NB the old GO:0003840 gamma-glutamyltransferase term is OBSOLETE) -> GGCT (O75223 PTHR12935, GO:0003839) -> OPLAH (O14841 PTHR11365, GO:0017168 ATP-dependent, regenerates glutamate, closing the cycle). A parallel intracellular GSH-degradation route: CHAC1 (Q9BUX1 PTHR12192, GO:0061928; ATF4/ER-stress-induced, pro-apoptotic/ferroptotic) -> 5-oxoproline + cysteinylglycine, also feeding OPLAH. GCLM is modelled with `processes` (non-catalytic modifier). GO term ids/labels verified against the local go.db. Downstream GSH-consuming enzymes (glutathione peroxidases GPX1/4, glutathione transferases) are separate modules. Disorders: hemolytic anemia (GCLC, GSR), GSS deficiency/5-oxoprolinuria, glutathionuria (GGT1), 5-oxoprolinase deficiency (OPLAH). ALIGN (YeastPathways project, 2026-10; GLUTATHIONESYN-PWY, PWYQT-4432, PWY3O-114 and PomBase 68b0f0d000008341): the human module was made eukaryote-wide. S. cerevisiae and S. pombe exemplars were added for GCL (GSH1, gcs1; S. pombe also has the GCLM-like gcs2, S. cerevisiae has none), GSS (GSH2, gsa1), GSR (GLR1, pgr1), ChaC (GCG1, ggg1) and 5-oxoprolinase (OXP1; S. pombe oxp1 and oxp2 are adjacent complete OPLAH-family paralogs). The GGT step became a ONE_OR_MORE compartment variant set (cell-surface GGT1 in animals vs vacuolar-membrane ECM38/ggt1/ggt2 in fungi). GGCT was made optional because neither yeast has a PTHR12935 member. Two parts were added: the Cys-Gly dipeptidase (DUG1/dug1/CNDP2, an M20A family; PMID:19346245) and the optional fungal Dug2-Dug3 glutamine-amidotransferase complex (PMID:22277648). YeastCyc corrections: OXP1, GCG1, GLR1 and DUG2/DUG3 are absent from the YeastCyc glutathione frames; the frame comments that no Cys-Gly dipeptidase gene or 5-oxoprolinase is known are out of date. GO-CAM disagreements: the SGD models place ECM38 in cytosol and give ECM38 and the Cys-Gly step only root or broad MF terms. Glutathione reductase is also used by the glutathione_thioredoxin_redox_systems module.

Connections

The gamma-glutamylcysteine made by GCL is the substrate for GSS.
GSH synthesised by GSS is (extracellularly) catabolised by GGT1.
GSH is also degraded intracellularly by CHAC1.
GSR keeps the glutathione pool reduced (GSSG -> 2 GSH), sustaining the GSH available for turnover.
The gamma-glutamyl-amino acids released by GGT1 are cyclised by GGCT.
The 5-oxoproline made by GGCT is hydrolysed to glutamate by OPLAH.
The 5-oxoproline released by CHAC1 is likewise converted to glutamate by OPLAH.
The glutamate regenerated by OPLAH re-enters GCL, closing the gamma-glutamyl cycle.
Cys-Gly released by GGT is hydrolysed by the Cys-Gly dipeptidase.
Cys-Gly released by ChaC enzymes is hydrolysed by the Cys-Gly dipeptidase.
Cytosolic GSH is cleaved by the Dug2-Dug3 complex (fungi).
Cys-Gly from Dug2-Dug3 is hydrolysed by Dug1.
Part 1: gamma-glutamylcysteine synthesis (rate-limiting)
Glutamate-cysteine ligase (GCLC catalytic + GCLM modifier)Reactionglutamate_cysteine_ligation

Annotons

GCLC: glutamate-cysteine ligase (catalytic subunit)
gclc_activity
Participant: Family: GCLC / glutamate-cysteine ligase catalytic family
Family:
GCLC / glutamate-cysteine ligase catalytic familyPANTHER:PTHR11164
Representative Members: GCLC (human)UniProtKB:P48506 GSH1 (Saccharomyces cerevisiae)UniProtKB:P32477 gcs1 (Schizosaccharomyces pombe)UniProtKB:Q09768

Function

glutamate-cysteine ligase activityGO:0004357
Substrates: L-glutamate L-cysteine ATP
Products: gamma-L-glutamyl-L-cysteine ADP + phosphate

Locations

cytosolGO:0005829

Ligates glutamate + cysteine to gamma-glutamylcysteine (rate-limiting).

GCLM: GCL modifier (regulatory) subunit
gclm_modifier
Participant: Family: GCLM / glutamate-cysteine ligase modifier family
Family:
GCLM / glutamate-cysteine ligase modifier familyPANTHER:PTHR13295
Representative Members: GCLM (human)UniProtKB:P48507 gcs2 (Schizosaccharomyces pombe)UniProtKB:O94246

Processes

glutathione biosynthetic processGO:0006750

Locations

cytosolGO:0005829

Non-catalytic modifier subunit (GO:1990609) forming the GCL holoenzyme (GO:0017109) with GCLC; lowers Km for glutamate/ATP and raises Ki for GSH feedback, greatly enhancing GCL efficiency.

Part 2: glutathione synthesis (glycine addition)
Glutathione synthetase (GSS)Reactionglutathione_synthesis

Annotons

GSS: glutathione synthetase
gss_activity
Participant: Family: GSS / glutathione synthetase family
Family:
GSS / glutathione synthetase familyPANTHER:PTHR11130
Representative Members: GSS (human)UniProtKB:P48637 GSH2 (Saccharomyces cerevisiae)UniProtKB:Q08220 gsa1 (Schizosaccharomyces pombe)UniProtKB:P35669

Function

glutathione synthase activityGO:0004363
Substrates: gamma-L-glutamyl-L-cysteine glycine ATP
Products: glutathione (GSH) ADP + phosphate

Locations

cytosolGO:0005829

Adds glycine to gamma-glutamylcysteine, forming glutathione.

Part 3: glutathione recycling (GSSG -> 2 GSH)
Glutathione-disulfide reductase (GSR)Reactionglutathione_recycling

Annotons

GSR: glutathione reductase (FAD/NADPH)
gsr_activity
Participant: Family: GSR / glutathione reductase (pyridine-nucleotide-disulfide oxidoreductase) family
Family:
GSR / glutathione reductase (pyridine-nucleotide-disulfide oxidoreductase) family
Representative Members: GSR (human)UniProtKB:P00390 GLR1 (Saccharomyces cerevisiae)UniProtKB:P41921 pgr1 (Schizosaccharomyces pombe)UniProtKB:P78965

Function

glutathione-disulfide reductase (NADPH) activityGO:0004362
Substrates: glutathione disulfide (GSSG) NADPH (FAD cofactor)
Products: glutathione (2 GSH) NADP+

Locations

cytosolGO:0005829

Regenerates reduced GSH from GSSG using NADPH (keeps the pool reduced).

Part 4: GSH breakdown by gamma-glutamyl transpeptidase (cell surface or vacuole)
gamma-glutamyl transpeptidase (GGT)Reactionextracellular_gsh_breakdown

Cleavage of the gamma-glutamyl bond of glutathione, at the cell surface in animals and at the vacuolar membrane in fungi.

Variant set: gamma-glutamyl transpeptidase compartment by compartment (lineage) (One Or More)
Cell-surface GGT (animals)Reactioncell_surface_ggt

Annotons

GGT1: gamma-glutamyltransferase (cell-surface)
ggt1_activity
Participant: Family: GGT / gamma-glutamyltransferase (Ntn-hydrolase) family
Family:
GGT / gamma-glutamyltransferase (Ntn-hydrolase) familyPANTHER:PTHR11686
Representative Members: GGT1 (human)UniProtKB:P19440

Function

glutathione gamma-glutamate hydrolase activityGO:0036374
Substrates: glutathione (extracellular; and GSH S-conjugates, leukotriene C4) H2O / amino-acid acceptor
Products: L-cysteinylglycine L-gamma-glutamyl-amino acid (or L-glutamate)

Locations

plasma membraneGO:0005886

Cleaves the gamma-glutamyl bond of extracellular GSH (-> cysteinylglycine).

Vacuolar-membrane GGT (fungi)Reactionvacuolar_ggt

Annotons

Vacuolar gamma-glutamyl transpeptidase (ECM38/CIS2; ggt1/ggt2)
fungal_vacuolar_ggt_activity
Participant: Family: GGT / gamma-glutamyltransferase (Ntn-hydrolase) family
Family:
GGT / gamma-glutamyltransferase (Ntn-hydrolase) familyPANTHER:PTHR11686
Representative Members: ECM38/CIS2 (Saccharomyces cerevisiae)UniProtKB:Q05902 ggt1 (Schizosaccharomyces pombe)UniProtKB:Q9US04 ggt2 (Schizosaccharomyces pombe)UniProtKB:O14194

Function

glutathione gamma-glutamate hydrolase activityGO:0036374
Substrates: glutathione (vacuolar; and glutathione S-conjugates) H2O / amino-acid acceptor
Products: L-cysteinylglycine L-glutamate or L-gamma-glutamyl-amino acid

Processes

glutathione catabolic processGO:0006751

Locations

fungal-type vacuole membraneGO:0000329

Initiates degradation of vacuolar glutathione and GSH S-conjugates; derepressed on poor nitrogen sources.

Part 5: gamma-glutamyl-amino acid cyclization (optional)

GGCT-family (PTHR12935) gamma-glutamylcyclotransferase has no member in S. cerevisiae or S. pombe, consistent with a truncated fungal cycle.

gamma-glutamylcyclotransferase (GGCT)Reactiongamma_glutamyl_cyclization

Annotons

GGCT: gamma-glutamylcyclotransferase
ggct_activity
Participant: Family: GGCT / gamma-glutamylcyclotransferase family
Family:
GGCT / gamma-glutamylcyclotransferase familyPANTHER:PTHR12935
Representative Members: GGCT (human)UniProtKB:O75223

Function

gamma-glutamylcyclotransferase activityGO:0003839
Substrates: (L-gamma-glutamyl)-L-amino acid
Products: 5-oxo-L-proline (pyroglutamate) L-amino acid

Locations

cytosolGO:0005829

Converts gamma-glutamyl-amino acids to 5-oxoproline + amino acid.

Part 6: intracellular GSH degradation (stress-induced)
Glutathione-specific gamma-glutamylcyclotransferase (CHAC1)Reactionintracellular_gsh_degradation

Annotons

CHAC1: glutathione-specific gamma-glutamylcyclotransferase
chac1_activity
Participant: Family: CHAC / glutathione-specific gamma-glutamylcyclotransferase family
Family:
CHAC / glutathione-specific gamma-glutamylcyclotransferase familyPANTHER:PTHR12192
Representative Members: CHAC1 (human)UniProtKB:Q9BUX1 GCG1 (Saccharomyces cerevisiae)UniProtKB:P32656 ggg1 (Schizosaccharomyces pombe)UniProtKB:P87305

Function

glutathione specific gamma-glutamylcyclotransferase activityGO:0061928
Substrates: glutathione (intracellular GSH)
Products: 5-oxo-L-proline (pyroglutamate) L-cysteinylglycine

Locations

cytosolGO:0005829

Degrades intracellular GSH to 5-oxoproline + cysteinylglycine.

Part 7: 5-oxoproline recycling (cycle closure)
5-oxoprolinase (OPLAH)Reactionoxoproline_to_glutamate

Annotons

OPLAH: 5-oxoprolinase (ATP-hydrolysing)
oplah_activity
Participant: Family: OPLAH / 5-oxoprolinase family
Family:
OPLAH / 5-oxoprolinase family
Representative Members: OPLAH (human)UniProtKB:O14841 OXP1 (Saccharomyces cerevisiae)UniProtKB:P28273 oxp1 (Schizosaccharomyces pombe)UniProtKB:Q10094 oxp2 (Schizosaccharomyces pombe)UniProtKB:Q10093

Function

5-oxoprolinase (ATP-hydrolyzing) activityGO:0017168
Substrates: 5-oxo-L-proline (pyroglutamate) ATP
Products: L-glutamate ADP + phosphate

Locations

cytosolGO:0005829

Hydrolyses 5-oxoproline to glutamate (regenerates the gamma-glutamyl donor).

Part 8: Cys-Gly hydrolysis (cysteine and glycine release)
Cys-Gly dipeptidase (DUG1/CNDP2 M20A family)Reactioncysgly_hydrolysis

Annotons

DUG1/CNDP2: Cys-Gly metallodipeptidase
dug1_cysgly_dipeptidase_activity
Participant: Family: M20A Cys-Gly dipeptidase (DUG1/CNDP2) clade
Family:
M20A Cys-Gly dipeptidase (DUG1/CNDP2) clade DUG1, S. pombe dug1 and human CNDP2 belong to PANTHER PTHR43270 (different subfamilies); that family also contains the non-catalytic DUG2 peptidase-like domain, so no family id is asserted.
Representative Members: DUG1 (Saccharomyces cerevisiae)UniProtKB:P43616 dug1 (Schizosaccharomyces pombe)UniProtKB:Q9P6I2 CNDP2 (human)UniProtKB:Q96KP4

Function

metallodipeptidase activityGO:0070573
Substrates: L-cysteinylglycine H2O
Products: L-cysteine glycine

Processes

glutathione catabolic processGO:0006751

Locations

cytosolGO:0005829

Releases cysteine and glycine from the Cys-Gly produced by GGT, ChaC and the Dug2-Dug3 complex.

Part 9: alternative cytosolic glutathione cleavage (DUG pathway; fungal) (optional)

Described in S. cerevisiae; the S. pombe dug2 assignment in the PomBase model (SPCC757.05c, PTHR43808) is in a different PANTHER family from S. cerevisiae DUG2 and is not used as an exemplar here.

Dug2-Dug3 glutamine-amidotransferase complexProtein Complexdug2_dug3_gsh_cleavage

The (Dug2-Dug3)2 complex cleaves glutathione into glutamate and Cys-Gly; Dug3 carries the catalytic class-II glutamine amidotransferase domain and Dug2 (WD40 plus inactive M20A domain) is required.

Annotons

DUG3: glutamine-amidotransferase subunit
dug3_gatase_activity
Participant: Gene Product: DUG3 (Saccharomyces cerevisiae)
Gene Product:
DUG3 (Saccharomyces cerevisiae)UniProtKB:P53871 S. cerevisiae DUG3/YNL191W.

Function

glutathione gamma-glutamate hydrolase activityGO:0036374
Substrates: glutathione H2O
Products: L-glutamate L-cysteinylglycine

Processes

glutathione catabolic processGO:0006751

Locations

cytosolGO:0005829

Catalytic subunit; the activity is realised only with Dug2 (contributes to GO:0036374 in GOA).

DUG2: WD40/M20A scaffold subunit
dug2_subunit
Participant: Gene Product: DUG2 (Saccharomyces cerevisiae)
Gene Product:
DUG2 (Saccharomyces cerevisiae)UniProtKB:P38149 S. cerevisiae DUG2/YBR281C; its M20A domain lacks peptidase activity.

Processes

glutathione catabolic processGO:0006751

Locations

cytosolGO:0005829

Non-catalytic partner required for Dug3-dependent glutathione cleavage.

PMID:22277648
Dug2p binds Dug3p through its WD40 domain and has no peptidase activity of its own.
PMID:17179087
DUG2 and DUG3 are required for degradation of GSH and gamma-Glu-Cys but not of normal-bond peptides.