Ketogenesis (hepatic ketone body synthesis)

Ketogenesis is the mitochondrial pathway, operating chiefly in liver during fasting, starvation, prolonged exercise and low-carbohydrate states, that converts acetyl-CoA (mostly from fatty-acid beta-oxidation) into the circulating ketone bodies acetoacetate and (R)-3-hydroxybutyrate, which supply oxidizable fuel to brain, heart and muscle when glucose is scarce. Four mitochondrial-matrix steps: mitochondrial acetyl-CoA acetyltransferase (thiolase, ACAT1) condenses two acetyl-CoA to acetoacetyl-CoA; the rate-limiting, fasting-induced mitochondrial HMG-CoA synthase (HMGCS2) adds a third acetyl-CoA to give 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA); HMG-CoA lyase (HMGCL) cleaves HMG-CoA to acetoacetate + acetyl-CoA; and the inner-membrane NAD+-dependent D-3-hydroxybutyrate dehydrogenase (BDH1) reversibly reduces acetoacetate to (R)-3-hydroxybutyrate, the predominant blood ketone. The pathway shares the HMGCL step with leucine catabolism and shares BDH1 (run in reverse) with ketolysis; liver exports the ketone bodies because it lacks the ketolytic enzyme OXCT1/SCOT. Inherited defects: HMGCS2 deficiency and HMGCL deficiency cause fasting hypoketotic hypoglycemia; ACAT1 (beta-ketothiolase) deficiency affects both ketone-body and isoleucine metabolism. (Ketone-body UTILIZATION/ketolysis in peripheral tissues — BDH1 -> OXCT1 -> ACAT1 -> 2 acetyl-CoA — is modelled separately in MODULE:ketone_body_oxidation.)

MODULE:ketogenesisDRAFTMetabolic Pathwaymodules/ketogenesis.yaml
ketone body biosynthetic processGO:0046951
GO:0046951
ketone body biosynthetic process
The module is grounded in the GO ketone body biosynthetic process (GO:0046951); each step is annotated within it.
Reactome:R-HSA-77111
Synthesis of Ketone Bodies
Step order and reaction stoichiometries follow the human Reactome "Synthesis of Ketone Bodies" pathway (R-HSA-77111): R-HSA-73916 (ACAT1), R-HSA-73918 (HMGCS2), R-HSA-74180 (HMGCL) and R-HSA-73912 (BDH1).
file:human/ACAT1/ACAT1-ai-review.yaml
ACAT1 gene review (human)
The thiolase step grounding (UniProtKB:P24752, GO:0003985 acetyl-CoA C-acetyltransferase activity) matches the completed human ACAT1 review.
file:human/HMGCS2/HMGCS2-ai-review.yaml
HMGCS2 gene review (human)
The rate-limiting HMG-CoA synthase step (UniProtKB:P54868, GO:0004421 hydroxymethylglutaryl-CoA synthase activity) matches the completed human HMGCS2 review.
file:human/HMGCL/HMGCL-ai-review.yaml
HMGCL gene review (human)
The HMG-CoA lyase step (UniProtKB:P35914, GO:0004419) matches the completed human HMGCL review (shared with leucine catabolism).
file:human/BDH1/BDH1-ai-review.yaml
BDH1 gene review (human)
The 3-hydroxybutyrate dehydrogenase step (UniProtKB:Q02338, GO:0003858) matches the completed human BDH1 review.
5Nodes
4Parts
0Variant Sets
0Variants
4Annotons
3Connections

Derived QC

Recommended-field compliance

100.0% recommended fields populated

All recommended fields populated.

Module deep research

✗ none found

No MODULE:ketogenesis 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.

Function consistency and core coverage

4 gene-function check(s) reflected in core functions · 0 conflict(s) · 2 evidence or coverage gap(s) (8 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
acat1_activity ACAT1 (human, mitochondrial)
UniProtKB:P24752
Family Representative 		acetyl-CoA C-acetyltransferase activity
GO:0003985 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
hmgcs2_activity HMGCS2 (human, mitochondrial/ketogenic)
UniProtKB:P54868
Family Representative 		hydroxymethylglutaryl-CoA synthase activity
GO:0004421 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
hmgcl_activity HMGCL (human)
UniProtKB:P35914
Family Representative 		hydroxymethylglutaryl-CoA lyase activity
GO:0004419 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
bdh1_activity BDH1 (human)
UniProtKB:Q02338
Family Representative 		3-hydroxybutyrate dehydrogenase activity
GO:0003858 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
acat1_activity Thiolase (acetyl-CoA C-acyltransferase) family (ACAT1)
PANTHER:PTHR18919
Family 		acetyl-CoA C-acetyltransferase activity
GO:0003985 		Family Supported
Family review supports GO:0003985 FAMILY_WIDE. Asserted by mevalonate_pathway and ketogenesis. It is the defining activity of the acetoacetyl-CoA thiolase subfamilies, and the long-chain thiolases also act on acetoacetyl-CoA, which is why their reviews retain it as non-core.
hmgcs2_activity HMG-CoA synthase family (HMGCS2/HMGCS1)
PANTHER:PTHR43323
Family 		hydroxymethylglutaryl-CoA synthase activity
GO:0004421 		Family Supported
Family review supports GO:0004421 FAMILY_WIDE. Asserted by mevalonate_pathway and ketogenesis; accepted by every reviewed member.
hmgcl_activity Hydroxymethylglutaryl-CoA lyase family (HMGCL)
PANTHER:PTHR42738
Family 		hydroxymethylglutaryl-CoA lyase activity
GO:0004419 		Family Review Missing
No supported structured family review is available for PANTHER:PTHR42738.
bdh1_activity 3-hydroxybutyrate dehydrogenase (SDR) family (BDH1)
PANTHER:PTHR43313
Family 		3-hydroxybutyrate dehydrogenase activity
GO:0003858 		Family Review Missing
No supported structured family review is available for PANTHER:PTHR43313.

Gene-review completeness (4/4 grounded genes reviewed)

3 complete review(s) · 0 with deep research · 0 missing review · 4 reviewed but lacking deep research

Gene Review Complete Deep research
ACAT1 P24752 ✓ 43/49 ✗
BDH1 Q02338 ✓ ✓ ✗
HMGCL P35914 ✓ ✓ ✗
HMGCS2 P54868 ✓ ✓ ✗

Details

Context
mitochondrial matrixGO:0005759 mitochondrial inner membraneGO:0005743
Ketogenesis (ketone body synthesis)Metabolic Pathwayketogenesis
ketone body biosynthetic processGO:0046951
Context
mitochondrial matrixGO:0005759 mitochondrial inner membraneGO:0005743

Four-step hepatic mitochondrial ketogenesis grounded to the human enzymes ACAT1 (UniProtKB:P24752, GO:0003985, EC 2.3.1.9), HMGCS2 (P54868, GO:0004421, EC 2.3.3.10), HMGCL (P35914, GO:0004419, EC 4.1.3.4) and BDH1 (Q02338, GO:0003858, EC 1.1.1.30). GO molecular-function/cellular-component terms were taken from the human GOA records; Reactome reaction ids and titles were verified against the local reactome cache. Each step uses a PANTHER family selector (generic over paralogs and orthologs) plus a concrete human representative member. Upstream, the acetyl-CoA substrate derives mainly from fatty-acid beta-oxidation; the HMGCL step is shared with leucine catabolism; and BDH1 plus the ketolytic enzyme OXCT1/SCOT run the reverse (utilization) pathway modelled in MODULE:ketone_body_oxidation. HMGCS2 is the mitochondrial/ketogenic isoform, distinct from the cytosolic mevalonate-pathway HMGCS1.

Connections

acat1_step -> hmgcs2_step Provides Input For
Acetoacetyl-CoA from ACAT1 is condensed with acetyl-CoA by HMGCS2.
hmgcs2_step -> hmgcl_step Provides Input For
HMG-CoA from HMGCS2 is cleaved by HMGCL.
hmgcl_step -> bdh1_step Provides Input For
Acetoacetate from HMGCL is reduced by BDH1 to (R)-3-hydroxybutyrate (the two are exported as the circulating ketone bodies).
Part 1: thiolytic condensation of two acetyl-CoA
2 acetyl-CoA to acetoacetyl-CoA + CoAReactionacat1_step

Annotons

ACAT1: acetyl-CoA acetyltransferase (thiolase)
acat1_activity
Participant: Family: Thiolase (acetyl-CoA C-acyltransferase) family (ACAT1)
Family:
Thiolase (acetyl-CoA C-acyltransferase) family (ACAT1)PANTHER:PTHR18919
Representative Members: ACAT1 (human, mitochondrial)UniProtKB:P24752

Function

acetyl-CoA C-acetyltransferase activityGO:0003985
Substrates: acetyl-CoA (x2)
Products: acetoacetyl-CoA coenzyme A

Locations

mitochondrial matrixGO:0005759

Condenses two acetyl-CoA to acetoacetyl-CoA (the reverse of its thiolytic role in isoleucine catabolism and ketolysis). ACAT1 deficiency (beta-ketothiolase deficiency) affects both ketone-body and isoleucine metabolism.

Part 2: rate-limiting HMG-CoA synthesis
acetoacetyl-CoA + acetyl-CoA to HMG-CoA + CoAReactionhmgcs2_step

Annotons

HMGCS2: mitochondrial HMG-CoA synthase
hmgcs2_activity
Participant: Family: HMG-CoA synthase family (HMGCS2/HMGCS1)
Family:
HMG-CoA synthase family (HMGCS2/HMGCS1)PANTHER:PTHR43323
Representative Members: HMGCS2 (human, mitochondrial/ketogenic)UniProtKB:P54868

Function

hydroxymethylglutaryl-CoA synthase activityGO:0004421
Substrates: acetoacetyl-CoA acetyl-CoA water
Products: (S)-3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) coenzyme A

Locations

mitochondrial matrixGO:0005759

Committed, rate-limiting, fasting-induced (PPARalpha/FGF21) ketogenic enzyme; the mitochondrial isoform, distinct from cytosolic HMGCS1 of mevalonate/cholesterol synthesis. Deficiency causes fasting hypoketotic hypoglycemia.

Part 3: cleavage to acetoacetate (shared with leucine catabolism)
HMG-CoA to acetoacetate + acetyl-CoAReactionhmgcl_step

Annotons

HMGCL: HMG-CoA lyase
hmgcl_activity
Participant: Family: Hydroxymethylglutaryl-CoA lyase family (HMGCL)
Family:
Hydroxymethylglutaryl-CoA lyase family (HMGCL)PANTHER:PTHR42738
Representative Members: HMGCL (human)UniProtKB:P35914

Function

hydroxymethylglutaryl-CoA lyase activityGO:0004419
Substrates: (S)-3-hydroxy-3-methylglutaryl-CoA (HMG-CoA)
Products: acetoacetate acetyl-CoA

Locations

mitochondrial matrixGO:0005759

Produces free acetoacetate. The same enzyme performs the terminal step of leucine catabolism (see the leucine_catabolism module); deficiency blocks both ketogenesis and leucine degradation.

Part 4: reduction to the predominant blood ketone
acetoacetate + NADH to (R)-3-hydroxybutyrate + NAD+Reactionbdh1_step

Annotons

BDH1: D-3-hydroxybutyrate dehydrogenase
bdh1_activity
Participant: Family: 3-hydroxybutyrate dehydrogenase (SDR) family (BDH1)
Family:
3-hydroxybutyrate dehydrogenase (SDR) family (BDH1)PANTHER:PTHR43313
Representative Members: BDH1 (human)UniProtKB:Q02338

Function

3-hydroxybutyrate dehydrogenase activityGO:0003858
Substrates: acetoacetate NADH
Products: (R)-3-hydroxybutyrate NAD+

Locations

mitochondrial inner membraneGO:0005743

Reversible, NAD+-dependent, phosphatidylcholine-requiring interconversion of acetoacetate and (R)-3-hydroxybutyrate; sets the ratio of the two circulating ketone bodies. The same enzyme run in reverse initiates ketolysis in peripheral tissues.