Purification and Properties of Arogenate Dehydrogenase from Actinoplanes missouriensis

Actinoplanes missouriensis utilizes arogenate as an intermediate in ʟ-tyrosine biosynthesis, while no evidence of prephenate dehydrogenase was observed. Arogenate dehydrogenase has been partially purified by a five-step procedure. The enzyme requires NAD as cofactor. The K values for NAD and arogenate are 0.2 mм and 0.15 mм, respectively. The molecular weight of arogenate dehydrogenase is about 68,000, and SDS gel electrophoresis indicates a composition of two identical subunits. The enzyme is not feedback inhibited by ʟ-tyrosine and unaffected by ʟ-phenylalanine, prephenate, phenylpyruvate, p-hydroxyphenylpyruvate or ʟ-tryptophan. Arogenate dehydrogenase is quite sensitive to p-hydroxymercuribenzoate with 50% inhibition at 12.5 μм of the SH -specific reagent. The presence of malate in usually applied arogenate preparations is demonstrated and the consequence of an impure substrate on arogenate dehydrogenase studies is discussed.