Interconversion of horse heart cytochrome C monomer and polymers.

When preparations of cytochrome c from mammalian species are chromatographed on columns of weak cation exchange agents, more than one chromatographic species can be obtained (1, 2). Only one of these fractions, that elutcd from the polycarboxylic resin Amberlite IRC-50 (Rohm and Hnas Company) at sodium or ammonium ion concentrations of 0.22 to 0.25 equivalent per liter (2, 3), can be considered to approximate the native protein (2). This fraction, termed Fraction I (2), exhibits the properties which distinguish cytochrome c from simple chemical hemochromogens. Thus, it is nonautoxidizable, does not react with carbon monoxide at pH values near neutrality, and has masimal electron transfer activity in various enzymic systems derived from the terminal oxidation chain (2, 4). Other fractions, collectively called Fraction II, can be eluted only at higher cation concentrations, react in varying degrees with oxygen and carbon monoxide, and have considerably lower activities than Fraction I in the succinate oxidase and cytochrome oxidase systems (2, 4). The present study reports the purification of three components of Fraction II of horse heart cytochrome c and their identification as a series of polymers of the monomeric Fraction I. It is also shown that the native protein can be transformed into a mixture of Fraction II components and that under appropriate conditions the polymers will revert to Fraction I, regaining completely the characteristic hemochromogen and electron transfer properties of the native protein. Preliminary accounts of this work have appeared (5, 6).