Terminal phenylalanine and tyrosine biosynthesis of Microtetraspora glauca

The enzymes of the terminal steps of the phenylalanine and tyrosine biosynthesis were partially purified and characterized in Microtetraspora glauca, a spore-forming member of the order Actinomycetales. This bacterium relies exclusively on the phenylpyruvate route for phenylalanine synthesis, no arogenate dehydratase activity being found. Prephenate dehydratase is subject to feedback inhibition by phenylalanine, tyrosine and tryptophan, each acting as competitive inhibitor by increasing the Km of 72 microM for prephenate. Based on the results of gel chromatography on Sephadex G-200, the molecular mass of about 110,000 Da is not altered by any of the effectors. The enzyme is quite sensitive to inhibition by 4-hydroxymercuribenzoate. Microtetraspora glauca can utilize arogenate and 4-hydroxyphenylpyruvate as intermediates in tyrosine biosynthesis. Prephenate and arogenate dehydrogenase activities copurifying from ion exchange columns with coincident profiles were detected. From gel-filtration columns the two activities eluted at an identical molecular-mass position of about 68,000 Da. The existence of a single protein exhibiting substrate ambiguity is consistent with the findings, that both dehydrogenases have similar chromatographic properties, exhibit cofactor requirement for NAD and are inhibited to the same extent by tyrosine and 4-hydroxymercuribenzoate.