KINETIC AND STRUCTURAL DIFFERENCES BETWEEN CYTOCHROME-C OXIDASES FROM BEEF-LIVER AND HEART

The cytochrome content of beef liver mitochondria differs from that of beef heart mitochodria by an 8-fold lower cytochrome aa3 and a 2-fold lower cytochrome b and c + c1 content. The kinetic properties of cytochrome c oxidases from beef liver and heart were measured with intact cytochrome c-depleted membranes, deoxycholate-dissolved membranes, and with the isolated enzymes at various cytochrome c concentrations with an oxygen electrode. Under all conditions a higher Vmax was found for the liver enzyme, both for the low- and high-affinity binding site for cytochrome c. Difference were also found for the Km of the 2 enzymes. Isolated beef heart mitochondria contained about twice as much cardiolipin than beef liver mitochondria. The isolated enzymes contained 1 mole of cardiolipin per mole of the heart enzyme, but 2 moles of cardiolipin per mole of the liver enzyme. By application of a high performance sodium dodecyl sulfate gel electrophoretic system the 2 isolated enzymes could be separated into 13 different protein components, 3 of which (polypeptides VIa, VIIa and VIII) differed in their apparent MW. The functional meaning of cytochrome c oxidase isoenzymes in liver and heart is disucssed.