Potentiometric and other studies on preparations of cytochrome c from ox- and horse-heart muscle

Abstract

E6 values at 25[degree] and pH 6.4 of both ox- and horse-heart cytochrome c purified by ion-exchange resin column chromatography were 0.255v; less pure preparations gave values higher by about 15 mv. A heme-containing impurity was consistently found in relatively large amounts in the final cytochrome c precipitate before dialysis according to the method of Keilin and Hartree (1945). The extent of incorporation of this impurity into the final cytochrome preparations varied with the conditions of dialysis. The most impure cytochromes were obtained by dialysis against ammonium hydroxide; this effect appears to be due to the alkalinity rather than to any specific action of ammonium ions. The purest preparations of reduced cytochrome c, obtained by purification on an ion-exchange resin column, showed insignificant autoxidation. The autoxidation of the less pure samples appeared to be largely dependent upon the level of heme impurity; the most impure cytochrome solutions became fully oxidized in air within 30 min. Spec-trophotometric results were used to assist in determining the degree of purity of the various cytochrome c preparations. Evidence was presented which throws considerable doubt upon the value of the Fe content as a criterion of purity.