Hydroxylamine dehydrogenase (EC 1.7.2.6, HAO (ambiguous)) is an enzyme with systematic name hydroxylamine:ferricytochrome-c oxidoreductase. This enzyme catalyses the following chemical reaction Hydroxylamine dehydrogenase (EC 1.7.2.6, HAO (ambiguous)) is an enzyme with systematic name hydroxylamine:ferricytochrome-c oxidoreductase. This enzyme catalyses the following chemical reaction The enzymes from the nitrifying bacterium Nitrosomonas europaea and the methylotrophic bacterium Methylococcus capsulatus are hemoproteins.