Reaction: PXLP-GCAT dimer ligates CoASH to 2A-3OB to form Gly and Ac-CoA
- in pathway: Threonine catabolism
The degradation of L-threonine to glycine in both prokaryotes and eukaryotes takes place through a two-step biochemical pathway. In the second step, mitochondrial 2-amino-3-ketobutyrate coenzyme A ligase (GCAT, aka KBL) catalyses the reaction between 2-amino-3-oxobutanoate (2A-3OBU) and coenzyme A (CoA-SH) to form glycine (Gly) and acetyl-CoA (Ac-CoA) (Edgar & Polak 2000). GCAT resides on the mitochondrial inner membrane and requires pyridoxal 5-phosphate (PXLP) as cofactor. It is strongly expressed in heart, brain, liver and pancreas. Dimeric GCAT:PXLP is thought to exist on the mitochondrial inner membrane in complex with tetrameric L-threonine 3-dehydrogenase (TDH), the first enzyme in this pathway (Tressel et al. 1986). With these two enzymes located together, it stops the rapid and spontaneous decarboxylation of 2A-3OBU to aminoacetone and carbon dioxide and instead, results in glycine formation.
Reaction - small molecule participants:
Gly [mitochondrial matrix]
H+ [mitochondrial matrix]
PPi [mitochondrial matrix]
Ac-CoA [mitochondrial matrix]
CoA-SH [mitochondrial matrix]
2A-3OBU [mitochondrial matrix]
ATP [mitochondrial matrix]
Reactome.org reaction link: R-HSA-6798345
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Reaction input - small molecules:
coenzyme A(4-)
L-2-amino-3-oxobutanoic acid zwitterion
ATP(4-)
Reaction output - small molecules:
glycine zwitterion
hydron
diphosphate(3-)
acetyl-CoA(4-)
Reactome.org link: R-HSA-6798345