Static measurements of the reaction of ligand binding were done by conventional spectrophotometry. The ligand-binding reactions with nitrated cytochrome c were performed with imidazole, iminazole, CO and NO. The stoicheiometry was found to be 1:1, and the stability constants for the complexes formed between the nitrated cytochrome c and the ligands are: 2.58 × 10(4) M-1 (imidazole); 1.01 × 10(2) M-1 (iminazole); 3.6 × 10(4) M-1 (CO); 2.74 × 10(4) M-1 (NO). It was found that the electrometric potentials at pH 7.0 and 25degreesC of [aminotyrosyl]cytochrome c are E'o form II = 0.115 V and E'o form I = 0.260 V, where forms I and II are two species of protein co-existing in the protein solution. The isoelectric point for the oxidized form of [nitrotyrosyl]cytochrome c was 10.05, at 4degreesC.

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