PXLP-GCAT dimer ligates CoASH to 2A-3OB to form Gly and Ac-CoA

Stable Identifier
Reaction [transition]
Homo sapiens
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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.

Literature References
PubMed ID Title Journal Year
3536927 Interaction between L-threonine dehydrogenase and aminoacetone synthetase and mechanism of aminoacetone production

Davis, L, Zieske, LR, Thompson, R, Menendez, MI, Tressel, T

J. Biol. Chem. 1986
10712613 Molecular cloning of the human and murine 2-amino-3-ketobutyrate coenzyme A ligase cDNAs

Edgar, AJ, Polak, JM

Eur. J. Biochem. 2000
Catalyst Activity

CoA-ligase activity of PXLP-GCAT dimer:TDH tetramer [mitochondrial inner membrane]

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