Open AccessConversion of Phenol Derivatives to Hydroxylated Products by Phenol Hydroxylase from Trichosporon cutaneum
Author(s) -
Peelen Sjaak,
Rietjens Ivonne M. C. M.,
Boersma Marelle G.,
Vervoort Jacques
Publication year - 1995
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1995.tb20386.x
Subject(s) - chemistry , hydroxylation , phenol , nucleophile , substrate (aquarium) , regioselectivity , phenols , substituent , molecular orbital , stereochemistry , photochemistry , catalysis , organic chemistry , enzyme , molecule , oceanography , geology
This study describes the regioselective hydroxylation and the rates of conversion of a series of fluorinated phenol derivatives by phenol hydroxylase from the yeast Trichosporon cutaneum. The natural logarithm of the k cat value for the conversion of the phenolic substrates correlates with the calculated energy of the reactive electrons in the highest occupied molecular orbital of the substrate ( r = 0.85). This observation supports the hypothesis that at physiological pH (7.6) and 25°C, in the absence of monovalent anions, the nucleophilic attack of the electrons in the highest occupied molecular orbital of the substrate on the C(4a)‐hydroperoxyflavin enzyme intermediate is of major importance in determining the overall rate of catalysis. Results from 19 F‐NMR analysis of the incubation mixtures demonstrate for phenols with two identical ortho substituents, that the ortho position which becomes preferentially hydroxylated is the one with the highest density of the reactive electrons in the highest occupied molecular orbital. A halogen substituent at a meta position decreases the chances for hydroxylation at the adjacent ortho position further than expected on the basis of the calculated reactivity. This result indicates a contribution of a protein/substrate dipolar interaction, influencing the time‐averaged orientation of the substrate with respect to the reactive C(4a)‐hydroperoxyflavin intermediate.