Utilization of formate as an additional energy source by glucose-limited chemostat cultures ofCandida utilis CBS 621 andSaccharomyces cerevisiae CBS 8066

The oxidation of benzene to phenol by whole cells of Nitrosomonas europaea is catalysed by ammonia monooxygenase, and therefore requires a source of reducing power. Endogenous substrates, hydrazine, hydroxylamine and ammonium ions were compared as reductants. The highest rates of benzene oxidation were obtained with 4 mM benzene and hydrazine as reductant, and equalled 6 mol· h^-1·mg protein^-1. The specificity of ammonia monooxygenase for benzene as a substrate was determined by measuring k _cat/K _m for benzene relative to k _cat/K _m for uncharged ammonia, a value of 0.4 being obtained. Phenol was found to be further hydroxylated to yield hydroquinone. This reaction, like benzene oxidation, was sensitive to the ammonia monooxygenase inhibitor allylthiourea. Catechol and resorcinol were not detected as products of phenol oxidation, implying that at least 88% of the hydroxylation is para-directed.