Cytochrome c554 as a possible electron donor in the hydroxylation of ammonia and carbon monoxide in Nitrosomonas europaea

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Abstract
The mechanism of ammonia oxidation was studied in the reconstituted system of N. europaea membrane fraction plus the N. europaea cytochrome c554. The cytochrome c554 was reduced by hydroxylamine, hydrazine and ammonia and the reduced cytochrome was oxidized upon the addition of ammonia or CO. The oxidation of CO in the presence of hydroxylamine or hydrazine was studied as a possible assay method for ammonia hydroxylase where hydroxylamine or hydrazine was supplying the reducing power required for the hydroxylation of CO. The stoichiometry of the reaction, Km values for substrates, and effects of pH and inhibitors were investigated. CO, a competitive inhibitor for ammonia oxidation, is an alternate substrate for ammonia hydroxylase using the reduced cytochrome c554 as the reducing power.