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Title: Non-stereospecific Transamination Catalyzed by Pyridoxal Phosphate-dependent Amino Acid Racemases of Broad Substrate Specificity (MOLECULAR BIOFUNCTION-Molecular Microbial Science)
Authors: Esaki, Nobuyoshi
Yoshimura, Tohru
Soda, Kenji
Lim, Young Hee
Keywords: Amino acid racemase
Stereochemistry
Pyridoxal phosphate
Issue Date: Mar-1999
Publisher: Institute for Chemical Research, Kyoto University
Journal title: ICR Annual Report
Volume: 5
Start page: 46
End page: 47
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 non-stereospecifically 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 a-ketoglutarate through the transamination with L-ornithine. Because glutamate does not serve as a substrate for racemization, the enzyme catalyzed the non-stereospecific overall transamination between L-ornithine and a-ketoglutarate. The cleavage and formation of the C-H bond at C-4' of the coenzyme and C-2 of the substrate thus occurs non-stereospecifically 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 non-stereospecific transamination.
URI: http://hdl.handle.net/2433/65185
Appears in Collections:Vol.5 (1998)

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