Development of New Methods on Isotope-Labeling of Amino Acid and Vitamin with Microbial Enzymes

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New methods on isotope-labeling of amino acid and vitamin were established with microbial enzymes, which have high stereo-specificity of reaction. First, or ^<35>S- labeling ofS-alkylcysteine was established by beta -replacement reaction of S-alkylcysleine alpha, beta -lyase, which was newly purified from a thermophile (Bacillus sp. 41A). Second, deuterium or tritium-labeling of D-amino acid was developed Stereoselectively with D-amino acid aminotransferase. Stereoselectively-deulerated NADH and NADPH were also prepared by coupling of glutamate racemase and glutamate dehydrogenase. Further, double isotope-labeling of Lysine was carried out by L-lysine epsilon -dehydrogenase and amino acid racemase. Finally. Substitution of S- (beta -aminoethyl) - cysteine for active-site lysine of thermostable aspartate aminotransferase was established by gene technology and chemical modification. Thus, many effective isotope-labeling of amino acid, vitamin and protein were developed.