FUNCTIONAL BINDING OF CARDIOLIPIN TO CYTOCHROME-C-OXIDASE

Bovine cytochrome c oxidase usually contains 3-4 mol of tightly bound cardiolipin per cytochrome aa3 complex. At least two of these cardioli pins are required for full electron transport activity. Without the ti ghtly bound cardiolipin, cytochrome c oxidase has only 40-50% of its o riginal activity when assayed in detergents that support activity, e.g ., dodecyl maltoside. By measuring the restoration of electron transpo rt activity, functional binding constants for cardiolipin and a number of cardiolipin analogues have been evaluated (K(d,app) = 1 muM for ca rdiolipin). These binding constants agree reasonably well with direct measurement of the binding using [C-14]-acetyl-cardiolipin (K(d) < 0.1 muM) when the enzyme is solubilized with Triton X-100. These data are discussed in relationship to the wealth of data that is known about t he association of cardiolipin with cytochrome c oxidase and the other mitochrondrial electron transport complexes and transporters.