The biosynthesis of phenylalanine and tyrosine; enzymes converting chorismic acid into prephenic acid and their relationships to prephenate dehydratase and prephenate dehydrogenase
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AbstractCell-free extracts of Aerobacter aerogenes and Escherichia coli were chromatographed on DEAE-cellulose and the eluates examined for some of the enzymes concerned in the conversion of chorismic acid into phenylalanine and tyrosine. Enzymes which are able to convert chorismate into prephenate (chorismate mutase) are eluted in two peaks of activity. The effects of phenylalanine and tyrosine on enzyme levels and activity showed that one of these enzymes (chorismate mutase P) is probably related to phenylalanine biosynthesis and the other (chorismate mutase T) to tyrosine biosynthesis. Chorismate mutase T travelled on DEAE-cellulose with prephenate dehydrogenase, (prephenate; NAD oxidoreductase (decarboxylating) the subsequent enzymic activity on the tyrosine biosynthetic pathway. The two activities were also affected simultaneously by mutation. Chorismate mutase P travelled on columns with the next enzymic activity on the pathway of phenylalanine biosynthesis, prephenate dehydratase, (prephenate hydro-lyase (decarboxylating)) and both activities were affected following mutation.In extracts of the A. aerogenes strain examined, but not in E. coli extracts, a second peak of prephenate dehydratase activity was eluted in the early column fractions. This activity, unlike the prephenate dehydratase travelling with chorismate mutase P is not inhibited by phenylalanine.It is suggested that, in the biosynthesis of phenylalanine and tyrosine, there are two enzymes or enzyme complexes metabolising chorismate, one leading through prephenate to phenylpyruvate and the other leading through prephenate to 4-hydroxyphenylpyruvate.

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