THE SITE OF THE REDOX-LINKED PROTON PUMP IN EUKARYOTIC CYTOCHROME-C OXIDASES

The electronic spectra of fully oxidized derivatives of some cytochrom e c oxidase preparations are distinctly pH dependent, In general, the observed spectral shifts are greater in the case of pulsed derivatives compared to resting preparations and also, greater for preparations o f the enzyme from shark skeletal muscle compared to beef heart. The lo w temperature near-infrared magnetic circular dichroism spectrum of th e fully oxidized shark enzyme is not pH dependent in the experimental range, indicating the sensitivity of the visible region electronic spe ctrum to variation in pH to be due principally to changes at the heme a(3)-Cu-B chromophore, The results are discussed in relation to propos ed mechanisms of proton translocation in cytochrome c oxidase.