Studies on the reduction of cytochrome c by thiols : A preliminary report

The reduction of cytochrome c by reduced glutathione is catalyzed by an impurity or impurities present in oxidized glutathione and cystine. In contrast to the conclusions arrived at by V. Massey, C. H. Williams, and G. Palmer [Biochem. Biophys. Res. Commun. 42, 730 (1971)], we conclude that this catalysis is not primarily caused by trisulfides. Heating of cystine or GSSG solutions results in a marked increase in the catalytic properties of the solutions. The formation of the catalytic compounds by heating is favored at alkaline pH, with an apparent pK value of about 9.0. The catalytic compounds appear to possess absorption spectra with maxima at 285 nm for GSSG solutions and 300 nm for cystine solutions. The compounds appear to be stable at pH values between 1.3 and 11. The identity of these compounds is presently being investigated.