Reaction of Nitrite and Cytochrome c in the Presence or Absence of Ascorbate

The reaction of nitrite with cytochrome c in the presence or absence of sodium ascorbate was studied. The amount of ferrocytochrome c nitrosyl compound I (cytochrome c · Fe 2+ ‐NO + ) formed in the absence of ascorbate was dependent on pH both at initial equal concentrations of nitrite or nitrous acid; the amount formed was very small at pH above 5.0. The presence of ascorbate significantly enhanced the extent of the reaction in the pH range 5.0–6.0. The reaction decreased rapidly at pH above 6.0, but application of heat was effective in giving a large formation of the product. Ascorbate reduced compound I to ferrocytochrome c nitrosyl compound II (cytochrome c · Fe 2+ ‐NO). The relative amounts of the two compounds formed was influenced by pH; at pH below 3.6, a mixture of compound I and II was formed, but only compound II was formed above pH 3.6. Compound II easily gave rise to ferrocytochrome c Cytochrome c probably reacts with nitrite in cured meat if ascorbate or erythorbate is used.