Reactions of Copper(I) with Micellar Porphyrins and Hemes. Spectroscopic Evidence for Copper(I)-Heme Binuclear Ion Formation

Article abstract of DOI:10.1021/ja00412a014

Addition of cuprous ion to sodium dodecyl sulfate solubilized porphyrins and ferrihemes containing olefinic substituent groups gives rise to spectral perturbations diagnostic of Cu(I) ? complexation.The hemes undergo slow subsequent demetalation in acidic solution, forming porphyrin dications; in the presence of high concentrations of Cu(II) ion the corresponding cupriporphyrins are also formed.For ferriprotoporphyrin IX, the rate of product formation is inversely dependent upon the Cu(II) ion concentration; the data are interpreted in terms of a reaction mechanism, the central feature of which is a dynamic equilibrium between oxidized and reduced hemes, i.e., Fe^IIIPPIX-Cu^I + Cu(I) = Fe^IIPPIX-Cu^I + Cu(II).This interpretation is supported by the observation that the hemes containing electron-withdrawing substituents in β-pyrrolic positions are extensively reduced to the ferro state by copper(I), but hemes lacking these groups remain primarily ferric when mixed with the cuprous reagent.The reduced Fe(II)-Cu(I) and mixed-valent Fe(III)-Cu(I) binuclear ions are discussed as potential structural models for the oxygen-binding site in cytochrome oxidase.