Characterization of nitrite-reducing activity in red blood cells (RBC) as a novel mechanism of nitric oxide (NO) formation in vivo

• Published in: Japanese Journal of Pharmacology 1998, Vol.76 (suppl.1), p.124-124
• Main Authors: Yoshioka, Toshimasa, Iwamoto, Noriko, Manno, Sumie, Takakuwa, Yuichi, Muraki, Takamura
• Format: Article
• Language: English
• ISSN: 0021-5198; 1347-3506
• DOI: 10.1016/S0021-5198(19)40616-1

Formation of nitrosyl hemoglobin following an intravenous injection of nitrite has been demonstrated in both clinical and experimental conditions. The present study examined the nature of this nitrite-reducing activity. Formation of NO was determined by an electron paramagnetic resonance spectrometry using N-methyl-D-glucaminedithiocarbamate (MGD), carboxyphenyltetra-methyl-imidazoline-oxyl or hemoglobin (Hb) as reagents for specific NO detection. RBC but serum exposed to nitrite showed NO formation. When RBC were separated into cytosolic and membrane preparations, NO formation from nitrite was exclusively demonstrated in the cytosols. The cytosolic fraction of nitrite-reducing activity was subjected to a time-of-flight mass spectrometry and an amino acid sequence analysis. The molecules detected in the fraction were Hb α and β. When purified human Hb was incubated with nitrite (0.1 to 10 mM), there was an increasing NO formation determined by MGD. Thus, the nitrite-reducing activity of RBC was at least in part dependent to hemoglobins. Hemoglobins may function not only as a carrier of NO as previously described but also as a reductant of nitrite to form NO.