Formation and Stability of Nitric Oxide Myoglobin I. Studies with Model Systems

Abstract

SUMMARY— The rate and extent of the formation of nitric oxide myoglobin (NOMb) were studied in aqueous model solutions containing 1–1.5 mg Mb per ml, to which various substances were added to study their effect. Conversion of Mb to NOMb was optimum when 1 mol sodium nitrite per mol Mb was present, provided that the solution contained optimum sodium ascorbate (200 mob). Results were the same with sodium erythorbate, ascorbic acid, and erythorbic acid. Cysteine also furthers the formation of NOMb; its optimum concentration was 100–200 mol per mol Mb, but even then the NOMb formation was appreciably lower than that found with ascorbate. The optimum nitrite concentration in the presence of cysteine was not less than 3 mols nitrite per mol Mb; this could be attributed to the chemical side reactions between nitrite and cysteine. Glutathion showed very little effect on the reaction between nitrite and Mb. The color intensity of NOMb was less in sodium chloride solution than in water. Sodium chloride also had an adverse effect on the formation of NOMb, but sodium nitrate and several sodium polyphosphates had no effect. Ferrous sulfate, on the other hand, accelerated the formation and produced a higher final concentration of nitric oxide myoglobin. Higher temperature and lower pH during the formation of NOMb both markedly accelerated its velocity, but the optimum quantities of NOMb formed were about the same. Investigations of the stability of NOMb in model solutions on exposure to light while in contact with air showed that the ratio between the concentrations of Mb, nitrite, and ascorbate and pH are the decisive factors, and that cysteine, glutathion, potassium nitrate, and polyphosphates had no effect in this respect.

Effect of Metal Ions on Residual Nitrite

“…If the nitrite depletion due to the addition of metal ions is a reductive process, it would seem logical that more nitric oxide would be produced leading to increased amounts of nitrosylhemochrome. It is well known that ferrous, ferric, cupric and zinc ions enhance the formation of cured color in model systems (Weiss et al 1953;Siedler and Schweigert 1959;Reith and Szakaly 1967). However, results in Fig.…”

“…Gibson (1943) showed that metal ions (CU++ and Fe"+) exerted a catalytic effect on the rate of reduction of methemoglobin in the presence of ascorbic acid. Since then, several studies have revealed the enhancing effect of metal ions such as Fe++, Fe"' , Cu++ and Zn"in the presence of ascorbic acid (Weiss et al 1953), and Fe++ in the presence of cysteine or ascorbic acid (Sielder and Schweigert 1959;Reith and Szakaly 1967) pigment. Seman et al (1980) showed that partial replacement of NaCl by MgC12 or KCl in bologna preparation was possible without impairing the functionality of NaCl.…”

Effect of sodium chloride on some of the chemical reactions of sodium nitrite in cured meat

“…In addition to measurable nitrite, another indication of formation of NOCl and increased nitrosating ability would be enhanced production of nitrosyl heme pigments due to increased production of the nitrosoreductant intermediates. If significant NOCl is formed, increased nitrosating activity should result in increased nitric oxide and subsequent nitrosyl heme formation Reith and Szakaly (1967a). reported that salt had an adverse effect on the color intensity and formation of nitrosylmyoglobin in model systems consisting of myoglobin, nitrite, ascorbate, and sodium chloride, whereasFujimaki et al (1975) showed that sodium chloride increased residual nitrite, enhanced development of color, and decreased the level of nitrate in model systems with the same components as mentioned previously but at different molar ratios.…”