Enzymatic Formation of Phenylpyruvic Acid in Pseudomonas Sp. (atcc 11299a) and Its Regulation.

The early steps in the biosynthesis of the aromatic amino acids in microorganisms leading to the formation of alicyclic precursors are rather well known (1, 2). Information regarding the regulation of these steps is beginning to accumulate (3, 4). A considerable gap, however, still exists in our knowledge about the properties and the regulation of the enzymes involved in the final aromatization steps in this pathway. The 1,4-cyclohexadienol, prephenic acid, is generally considered to be the branchpoint in the formation of phenylalanine and tyrosine. Prephenic acid is converted in the presence of the enzyme prephenate dehydratase (prephenate hydrolase (decarboxylating)) (or in acidic medium in a spontaneous dienol-benzene rearrangement) (5) to phenylpyruvic acid (6). Alternatively, in the presence of prephenate dehydrogenase (prephenate : NAD oxidoreductase (decarboxylating)) and DPN, p-hydroxyphenylpyruvic acid is the product (7) (an oxidative aromatization reaction). Although the enzymatic conversion of prephenic acid to phenylpyruvate has been demonstrated, no work has appeared concerning the purification, characteristics, and regulation of the responsible enzyme. During a study of the inducible phenylalanine hydroxylase of Pseudomonas sp. (ATCC 11299a) (8), it was considered of interest to investigate the possible regulation of the enzymes involved in the synthesis of the aromatic amino acids in these induced cells. This report concerns the purification, properties, and regulation of prephenate dehydratase. The studies to be described include descriptions of the characteristics of the enzyme, the feedback inhibition by phenylalanine, and the feedback stimulation of the enzyme by tyrosine.