NITRITE METABOLISM BY MUSCLE IN VITRO.

Abstract

Abstract 1. 1. The anaerobic incubation of minces of fresh pig muscles at pH 6.0 with sodium nitrite, but not with potassium nitrate, resulted in the evolution of a gas fraction which was insoluble in alkali but was soluble in alkaline sulphite, corresponding in solubility properties to nitric oxide. 2. 2. Nitric oxide was identified as a product of the anaerobic incubation of muscle minces with sodium nitrite at pH 6.0 by mass spectrometry and infrared spectrophotometry; its presence was also recognised by a new technique involving the increased absorbancy in the ultraviolet of the alkaline sulphite absortion liquors and by the conversion of indigenous haem pigment to nitrosylmyoglobin. 3. 3. The output of the nitric oxide gas fraction was unaffected by the inclusion of the antibiotics aureomycin and chloromycetin and neither the aerobic nor the anaerobic development of the small resident bacterial populations of fresh muscle minces resulted in the enhancement of their capacities to reduce nitrite to nitric oxide, whereas the reduction of nitrate was apparent only with tissues in which bacterial growth had been deliberately encouraged. 4. 4. The formation of the nitric oxide gas fraction was markedly reduced by heat treatment of the minces at 56° and 80°, was dependent upon nitrite concentration and was stimulated by reduced methylene blue; this and other evidence indicates that nitrite is able to compete with other electron acceptors for the reductive processes of the mammalian respiratory enzyme systems. No direct interaction at pH 6.0 was observed between NaNO2 and Hb, Mb, GSH and ferrocytochrome c.