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).

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.
8Nodes
7Parts
0Variant Sets
0Variants
8Annotons
8Connections

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.

Gene-review completeness (8/8 grounded genes reviewed)

8 complete review(s) · 2 with deep research · 0 missing review · 6 reviewed but lacking deep research

Gene Review Complete Deep research
CHAC1 Q9BUX1 ✓ ✓ ✗
GCLC P48506 ✓ ✓ ✓
GCLM P48507 ✓ ✓ ✗
GGCT O75223 ✓ ✓ ✗
GGT1 P19440 ✓ ✓ ✗
GSR P00390 ✓ ✓ ✗
GSS P48637 ✓ ✓ ✓
OPLAH O14841 ✓ ✓ ✗

Details

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

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).

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.
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

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

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

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) familyPANTHER:PTHR42737
Representative Members: GSR (human)UniProtKB:P00390

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: extracellular GSH breakdown (gamma-glutamyl transfer)
gamma-glutamyltransferase 1 (GGT1)Reactionextracellular_gsh_breakdown

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).

Part 5: gamma-glutamyl-amino acid cyclization
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

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 familyPANTHER:PTHR11365
Representative Members: OPLAH (human)UniProtKB:O14841

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).