3,4-dihydroxystyrene, a novel microbial inhibitor for phenylalanine hydroxylase and other pteridine-dependent...

A new microbial inhibitor for rat-liver phenylalanine hydroxylase (L-phenylalanine, tetrahydropteridine: oxygen oxidoreductase (4-hydroxylating), EC 1.14.16.1) was isolated from a culture medium of Fomes tasmanicus, and its structure was determined as 3,4-dihydroxystyrene. This compound inhibited the enzyme by 50% at a concentration of 5 X 10(-6) M and 5 X 10(-7) M, respectively, without or with preincubation at 25 degrees C for 15 min. Without preincubation, dihydroxystyrene inhibited phenylalanine hydroxylase noncompetitively with phenylalanine and a pteridine cofactor, 6,7-dimethyltetrahydropterin, and uncompetitively with oxygen. A change in kinetic properties of the inhibition was observed when the enzyme was preincubated with dihydroxystyrene; the degree of inhibition was increased, and the purely noncompetitive-type inhibition with phenylalanine changed to a mixed-type inhibition. A study concerning the structure-inhibitory activity relationship using several compounds similar to dihydroxystyrene, indicated that the catechol structure is essential and that the structure of the aliphatic side-chain affects the inhibitory potency. A similar degree of inhibition was observed using 6,7-dimethyl- or 6-methyltetrahydropterin or tetrahydrobiopterin as a cofactor. Dihydroxystyrene also inhibited other pteridine-dependent monooxygenases, tyrosine hydroxylase (EC 1.14.16.2) and tryptophan hydroxylase (EC 1.14.16.4), indicating that dihydroxystyrene is a general inhibitor for pteridine-dependent monooxygenases.