Studies of aromatic hydroxylation

The conversion of [4-3H]- and [4-3H; 3,5-2H2]-phenyl-alanine into tyrosine by cultures of Pseudomonas sp. (NCIB 9289) has been studied. Fromm a consideration of the degree of retention of tritium observed during the hydroxylation of the two precursors a kinetic isotope effect, kD/kT = 2.8 ± 0.1 (kH/kD = 10 ± 1), has been calculated for the final aromatisation process following the NIH shift. The relevance of this result to the overall reaction pathway is discussed in the light of similar data derived from possible chemical models for the biological process. [Continues.]