Nonstereospecific transamination catalyzed by pyridoxal phosphate- dependent amino acid racemases of broad substrate specificity

Young Hee Lim, Tohru Yoshimura, Yoichi Kurokawa, Nobuyoshi Esaki, Kenji Soda

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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 α-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 α-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.

Original languageEnglish
Pages (from-to)4001-4005
Number of pages5
JournalJournal of Biological Chemistry
Issue number7
Publication statusPublished - 1998 Feb 13


ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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