Cytochrome c Oxidase Components V. A CYTOCHROME a PREPARATIOK FREE OF CYTOCHROME us*

Despite considerable spectral evidence supporting the concept of two cytochromes, a and a3, in the terminal respiratory system (l-15), there has not been uniform agreement that the mammalian cytochrome c osidase system contains these two cytochromes (16-18). Recent work which distinguished these cytochromes chemically has strengthened the spectral observations (19, 20). It was possible by the use of borohydride under special conditions to alter the prost,hetic group of cytochrome a3 without affecting the prosthetic group of cytochrome a. The present work is an estension of these observations. One of the classical methods employed in protein purification procedures is the selective destruction of contaminating proteins. By applying such a procedure, it has been possible to prepare cytochrome a free of cytochrome a3. It is the purpose of this paper to present the method of preparation as well as define some of the properties of a preparation of cytochrome a free of cytochrome ~3.