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Title: | Stereospecificity of Thermostable Ornithine 5-Aminotransferase for the Hydrogen Transfer in the L- and D-Ornithine Transamination (MOLECULAR BIOFUNCTION-Molecular Microbial Science) |
Authors: | Esaki, Nobuyoshi Yoshimura, Tohru Soda, Kenji Jhee, Kwang-Hwan |
Keywords: | Stereochemistry Ornithine transaminase Pyridoxal phosphate |
Issue Date: | Mar-1997 |
Publisher: | Institute for Chemical Research, Kyoto University |
Journal title: | ICR Annual Report |
Volume: | 3 |
Start page: | 46 |
End page: | 47 |
Abstract: | The thermostable ornithine 5-aminotransferase of a thermophile, Bacillus sp. YM-2 is unique in acting on both enantiomers of ornithine, although less effectively on the D-enantiomer. We studied the stereospecificity of the enzyme for the hydrogen abstraction from C-5 of the substrate moiety and the addition and removal of the hydrogen at C-4' of the cofactor (pyridoxal phosphate and pyridoxamine phosphate) moiety of the external Schiff base intermediate in the transamination of L- and D-ornithine. [5- 3H]L- and D-ornithines were prepared by incubation of L- and D-ornithines with the B. sp. YM-2 ornithine 5-aminotransferase in 3H2O, respectively. The C-5 of the tritiated L-and D-ornithine was proved to have the S-configuration with L-ornithine 5-aminotransferase of a mesophile, Bacillus sphaericus, catalyzing the stereospecific abstraction of pro-S hydrogen from C-5 of L-ornithine and amino acid racemase with lowsubstrate specificity of Pseudomonas putida . When apo-form of the enzyme was incubated with pyridoxamine 5'-phosphates that was stereospecifically tritiated at C-4' and 2-oxoglutarate in the presence of L-ornithine or D-ornithine, tritium was released exclusively from (4'S)-[4'-3H] pyridoxamine. These results suggest that the B. sp. YM-2 ornithine 5-aminotransferase stereospecifically abstracts the pro-S hydrogen from C-5 of L- and D-ornithine. The hydrogen abstracted is then transferred to C-4' of the cofactor moiety stereospecifically on the si face of the external Schiff base intermediate irrespective of the C-2 configuration of amino donor. |
URI: | http://hdl.handle.net/2433/65103 |
Appears in Collections: | Vol.3 (1996) |

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