Hydroxylation of phenylalanine by Pseudomonas sp.: measurement of an isotope effect following the NIH shift

Abstract

The conversion of [4-³H]- and [4-³H;3,5-²H₂]phenylalanine into tyrosine by cultures of Pseudomonas sp. (ATCC 11 299a) has been studied. Comparison of the tritium retentions observed during hydroxylation of the two precursors showed an isotope effect, k_D/k_T= 2·8 ± 0·1 (k_H/k_D= 10 ± 1), for the final aromatisation reaction following the NIH shift. This value is compared with those of likely chemical models for the biochemical process.