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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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