Studies on the electron-transfer system LX. Molecular weights of some components of the electron transfer chain in beef-heart mitochondria

Abstract

The molecular weights of two enzyme complexes purified from beef-heart mitochondria have been determined by the light-scattering technique. The enzymes studied were coenzyme QH2-cytochrome c reductase (Complex III) and cytochrome c oxidase (cytochrome c:O2 oxidoreductase, EC 1.9.3.1) (Complex IV). The weight average molecular weight of Complex III from light-scattering data agrees closely with the minimal molecular weight estimated from the cytochrome c1 content. In the case of cytochrome oxidase, however, the molecular weight was about two times larger than the minimal molecular weight based on the cytochrome a content. This observation supports the view that there are two heme a prosthetic groups per molecule of cytochrome oxidase.