BOVINE HEART CYTOCHROME-C OXIDASE PREPARATIONS CONTAIN HIGH-AFFINITY BINDING-SITES FOR MAGNESIUM AS WELL AS FOR ZINC, COPPER, AND HEME IRON

Metal contents of 6 bovine heart cytochrome c oxidase preparations were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). Mg is present in consistent amounts reflected by Fe/Mg and Mg/Zn ratios of 2.06 .+-. 0.18 and 1.10 .+-. 0.14, respectively. More Cu than Fe is always present; the average Cu/Fe atom ratio is 1.27 .+-. 0.10. Ca is found in significant but variable amounts. Mg, Zn, Fe and Cu are each bound with high affinity as shown by a resistance to removal upon dialysis against various media. The Cu in excess of Fe, the Mg and the Zn may each have catalytic and/or structural roles in the oxidase. The observed metal stoichiometry suggests that a dimeric catalytic unit with 5 Cu, 4 Fe, 2 Zn, and 2 Mg may be present in the inner mitochondrial membrane to carry out O2 reduction and H+ pumping.