Mechanism of reversible glycine cleavage reaction in Arthrobacter globiformis. Function of lipoic acid in the cleavage and synthesis of blycine

Kochi, H.; Kikuchi, G.

Archives of Biochemistry and Biophysics 173(1): 71-81


ISSN/ISBN: 0003-9861
PMID: 1259444
DOI: 10.1016/0003-9861(76)90236-8
Accession: 026941070

Download citation:  

Article/Abstract emailed within 0-6 h
Payments are secure & encrypted
Powered by Stripe
Powered by PayPal

The hydrogen carrier protein (H-protein) from Arthrobacter globiformis was found to contain one lipoic acid residue per molecule. In the glycine cleavage reaction, H-protein could be replaced by lipoic acid and in glycine synthesis, by dihydrolipoic acid. Lipoamide was less effective than lipoic acid in substituting for H-protein. In glycine synthesis with dihydrolipoic acid, even tetrahydrofolate and T-protein, an enzyme catalyzing the tetrahydrofolate-dependent step of the reaction, were not required, and the whole process of glycine synthesis could proceed in the presence of only one enzyme, P-protein, a pyridoxal phosphate-requiring enzyme. In the glycine decarboxylation reaction with lipoic acid, the decarboxylation product seemed to be bound to lipoic acid, possibly in the SCH2NH2 form, which was extractable with benzene. The suspected intermediate compound could also be formed nonenzymically from dihydrolipoic acid, formaldehyde and ammonia, and glycine was obtained when the benzene extract containing the suspected intermediate compound was incubated with P-protein and NaHCO3. Several lines of evidence suggest that a thiol group of dihydrolipoic acid reacts first with formaldehyde to form a hemimercaptal or mercaptal to which ammonia is subsequently fixed; the binding of ammonia, however, appears to be unstable. Based on observations with free lipoic acids, the sequence of the T-protein-dependent reaction steps in the enzymic, reversible glycine cleavage reaction is discussed.