Reduction by dithionite ion of adducts of metmyoglobin with imidazole, pyridine, and derivatives

The rate and equilibrium constants for the information of a number of metmyoglobin species Mb+X (X = imidazole, imidazole-H-, 1-methylimidazole, 2-methylimidazole, 4-nitroimidazole, 2-methyl-5-nitroimidazole, pyridine, 2-, 3-, and 4-picoline) and the rates of their reduction by dithionite have been measured at 25 degrees. Several different kinds of kinetic behavior for the reduction were observed. In all cases, a rate constant for direct reaction of Mb+X with SO2- can be assessed. The data strongly support attack of SO2- on the ligand, followed by electron transfer through the pi system to the metal ion.