Metal‐Free and Metal‐Substituted Cytochromes c. Use in Characterization of the Cytochrome c Binding Site

Abstract

The luminescent properties of metal‐free, tin(IV) and zinc(II) cytochromes c have been used to characterize the interaction of cytochrome c with mitochondria and cytochrome oxidase. Diminution in the fluorescence yields of tin and zinc cytochrome c occur when these derivatives bind to cytochrome oxidase or mitochondria. Based upon spectral overlap and quantum yield, the distance between the porphyrin rings of cytochrome a and cytochrome c is estimated according to Forster theory to be in the neighborhood of 3.5 nm. Measurements of the polarized emission of metal‐free ‘porphyrin’ cytochrome c when bound to oriented layers of cytochrome c oxidase indicate that the porphyrin is bound obliquely to the plane of the oxidase layers with an angle of about 70°C from heme plane to membrane plane. It is proposed that these data have significance for elucidation of electron transfer mechanisms. Copyright © 1977, Wiley Blackwell. All rights reserved