Nitrification Mechanisms\nfor the P460 Enzymes

The oxidation of hydroxylamine was studied by quantum\nchemical\nmodeling. Hydroxylamine is the product of ammonia oxidation in ammonia\nmonooxygenase. That mechanism has been studied recently by quantum\nchemical modeling as here. Only two enzymes can oxidize hydroxylamine,\nhydroxylamine oxidase and cytochrome-P460. Both employ the unusual\nP460-heme cofactor. In hydroxylamine oxidase, there is a covalently\nlinked tyrosine, while in cytochrome-P460, there is a covalently linked\nlysine. The calculations give explanations for the experimental findings\nthat NO is the final product in hydroxylamine oxidase, while N<sub>2</sub>O is the final product in cytochrome-P460. The effect of the\ncovalent attachments has been investigated, and reasons for their\npresence have been given. The methodology used, which was proven to\ngive very good agreement with experiments for several redox enzymes,\nagain leads to excellent agreement with experimental findings.