NITRIC-OXIDE FORMATION FROM HYDROXYLAMINE BY MYOGLOBIN AND HYDROGEN-PEROXIDE

Hydroxylamine (HA), which is a natural product of mammalian cells, has been shown to possess vasodilatory properties in several model system s. In this study, HA and methyl-substituted hydroxylamines, N-methylhy droxylamine (NMHA) and N,N-dimethylhydroxylamine (NDMHA), have been te sted for their ability to generate free diffusible nitric oxide (NO) i n the presence of myoglobin (Mb) and hydrogen peroxide. A NO-specific conversion of nyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carb oxy-PTIO) to rboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl (carbo xy-PTI), measured by electron spin resonance (ESR) spectroscopy, along with nitrite and nitrate production, was observed for HA but not for NMHA and NDMHA. ESR measurements at 77 K showed the formation of the f errous nitrosyl myoglobin, Mb-NO, in the reaction mixtures containing Mb, H2O2 and HA. Our data also demonstrate that Mb-NO is an end produc t of the reaction pathway involving Mb, H2O2 and HA, rather than a rea ction intermediate in the formation of NO. In summary, our results dem onstrate a possible pathway of NO formation from HA, however, the sign ificance of this mechanism for bioactivation of HA in vivo is unknown at the present time. (C) 1997 Elsevier Science B.V.