Xanthine oxidase (XO) was shown to catalyze the reduction of nitrite to nitric oxide (NO),
under anaerobic conditions, in the presence of either NADH or xanthine as reducing
substrate. NO production was directly demonstrated by ozone chemiluminescence and
showed stoichiometry of approximately 2: 1 versus NADH depletion. With xanthine as
reducing substrate, the kinetics of NO production were complicated by enzyme inactivation,
resulting from NO-induced conversion of XO to its relatively inactive desulfo-form. Steady …