Abstract
d-phenylglycine aminotransferase ( d-PhgAT) from a newly isolated soil bacterium, Pseudomonas stutzeri ST-201, was purified to electrophoretic homogeneity and characterized. The molecular weight ( M r) of the native enzyme was estimated to be 92 000. It is composed of two subunits identical in molecular weight ( M r=47 500). The isoelectric point (p I) of the native enzyme was 5.0. The enzyme catalyzed reversible transamination specific for d-phenylglycine or d-4-hydroxyphenylglycine in which 2-oxoglutarate was an exclusive amino group acceptor and was converted into l-glutamic acid. Neither the d- nor l-isomer of phenylalanine, tyrosine, alanine, valine, leucine, isoleucine or serine could serve as a substrate. The enzyme was most active at alkaline pH with maximum activity at pH 9–10. The temperature for maximum activity was 35–45°C. The apparent K m values for d-phenylglycine and for 2-oxoglutarate at 35°C, pH 9.5 were 1.1 and 2.4 mM, respectively. The enzyme activity was strongly inhibited by typical inhibitors of pyridoxal phosphate-dependent enzymes. Possible application of this enzyme for synthesis of enantiomerically pure d-phenylglycine was demonstrated.
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