Cytochrome and intracellular oxidase

Abstract

Solutions may be prepared containing cysteine, heart-muscle oxidase preparation and the c component of cytochrome extracted from bakers'' yeast cells, in which cytochrome c becomes rapidly oxidized on shaking and reduced again on standing. This behavior is similar to that of cytochrome in living yeast cells. Neither oxidase alone nor cytochrome c alone causes the oxidation of cysteine, but mixtures of the 2 cause rapid oxidation. Except for low concentrations of oxidase, the rate of oxidation of cysteine is approximately proportional to the square-root of the oxidase concentration when the cytochrome c concentration is kept constant and to the square-root of the cytochrome c concentration when the oxidase concentration is kept constant. Thus, the rate seems to approximately follow the so-called rule of Schutz. With the low oxidase concentrations, the rate is directly proportional to the concentration. With different concentrations of a given oxidase-cytochrome c mixture, the rate is a linear function of the concentration except for very low values. Warming to above 70[degree] C. abolishes the activity of the oxidase-cytochrome c mixtures. It is almost completely inhibited by 0.001 M. KCN and 80-87 per cent inhibited in the presence of 0.001 M. Na2S. It is greatly inhibited in the dark by high concentrations of CO. This inhibition is diminished by strong light. The Warburg partition constant is 8-10 for the dark reaction and 63 for the light reaction. Ure-thane has no effect on the activity of oxidase-cytochrome c mixtures. Thus the catalytic system reconstructed from the oxidase of heart-muscle and cytochrome c from yeast cells behaves like a true respiratory system of a cell. Oxidase itself does not directly catalyze the oxidation of cysteine. It reacts with the non-autoxidizable cytochrome c to form the active catalytic system.