DISMUTATION OF HYDROXYLAMINE TO AMMONIA AND NITRITE BY A NOVEL, MEMBRANE-BOUND ENZYME FROM THE CYANOBACTERIUM PHORMIDIUM-UNCINATUM

Extracts from ammonium-grown phototrophic cultures of Phormidium uncinatum exhibited a catalytic and stoichiometric formation of nitrite and ammonia from hydrogen peroxide and hydroxylamine. This reaction was due to a novel enzyme (referred to as hydroxylamine dismutase), which was bound to the heavier thylakoid membranes. The enzyme was solubilized from the membranes by detergent treatment and further purified by ion-exchange chromatography. On the basis of inhibitor studies, the involvement of metal ions and sulfhydryl groups in the characteristic reaction is suggested. © 1990.