PMID:9461589
| Citation |
Lim, YH, Yoshimura, T, Kurokawa, Y, Esaki, N and Soda, K (1998) Nonstereospecific transamination catalyzed by pyridoxal phosphate-dependent amino acid racemases of broad substrate specificity. J. Biol. Chem. 273:4001-5 |
|---|---|
| Abstract |
Pyridoxal 5'-phosphate-dependent amino acid racemases of broad substrate specificity catalyze transamination as a side reaction. We studied the stereospecificities for hydrogen abstraction from C-4' of the bound pyridoxamine 5'-phosphate during transamination from pyridoxamine 5'-phosphate to pyruvate catalyzed by three amino acid racemases of broad substrate specificity. When the enzymes were incubated with (4'S)- or (4'R)-[4'-3H]pyridoxamine 5'-phosphate in the presence of pyruvate, tritium was released into the solvent from both pyridoxamine 5'-phosphates. Thus, these enzymes abstract a hydrogen nonstereospecifically from C-4' of the coenzyme in contrast to the other pyridoxal 5'-phosphate-dependent enzymes so far studied, which catalyze the stereospecific hydrogen removal. Amino acid racemase of broad substrate specificity from Pseudomonas putida produced D- and L-glutamate from alpha-ketoglutarate through the transamination with L-ornithine. Because glutamate does not serve as a substrate for racemization, the enzyme catalyzed the nonstereospecific overall transamination between L-ornithine and alpha-ketoglutarate. The cleavage and formation of the C-H bond at C-4' of the coenzyme and C-2 of the substrate thus occurs nonstereospecifically on both sides of the plane of the coenzyme-substrate complex intermediate. Amino acid racemase of broad substrate specificity is the first example of a pyridoxal enzyme catalyzing nonstereospecific transamination. |
| Links | |
| Keywords |
Amino Acid Isomerases/metabolism; Bacterial Proteins/metabolism; Catalysis; Hydrogen/metabolism; Ketoglutaric Acids/metabolism; Molecular Conformation; Ornithine/metabolism; Pseudomonas putida/enzymology; Pyridoxal Phosphate/pharmacology; Pyridoxamine/analogs & derivatives; Pyridoxamine/metabolism; Pyruvic Acid/metabolism; Substrate Specificity; Transaminases/metabolism |
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