Phenylalanine hydroxylase from Pseudomonas sp. (ATCC 11299a). Purification, molecular weight, and influence of tyrosine metabolites on activation and hydroxylation.

Phenylalanine hydroxylase from Pseudomonas sp. (ATCC 11299a) has been purified 25- to 30-fold by a procedure which has been modified from that previously described for this organism (Guroff, G., and Ito, T. (1965) J. Biol. Chem. 240, 1175-1184; Guroff, G., and Rhoads, C. A. (1967) J. Biol. Chem. 242, 3641-3645). Further purification yielded a preparation which was judged to be about 80% pure by sodium dodecyl sulfate-containing and standard analytical polyacrylamide gels, but the activity in this preparation has proved to be very labile. The enzyme appears to be a single protein chain of between 25,000 to 27,000 molecular weight. Phenylalanine, tyrosine, and tryptophan inhibit the activation of the enzyme by iron in a competitive fashion. The tyrosine metabolites, p-hydroxyphenylpyruvic and homogentisic acids exhibit a biphasic effect on activation, stimulating at low iron, and inhibiting at higher iron concentrations. The hydroxylation itself is inhibited by tyrosine and related compounds such as L-3,4-dihydroxyphenylalanine and dopamine. p-Hydroxyphenylpyruvic acid is a competitive inhibitor with respect to both substrate and cofactor. The data indicate a variety of means by which the bacterium can regulate phenylalanine hydroxylation.