Studies on cytochrome oxidase. Preliminary characterization of an enzyme containing only four subunits

The preparation of a four-subunit enzyme from yeast, capable of catalyzing the oxidation of ferrocytochrome c, is described. It is derived from proteins containing seven or five subunits by means of recycling exclusion chromatography in the presence of 0.1% sodium dodecyl sulfate. Its catalytic properties are similar to those of the parent enzyme. Gel electrophoresis of this preparation in the presence of sodium dodecyl sulfate reveals three bands, migrating with RF values that correspond to molecular weights of 14.6, 12.3, and 10.6 X 10(3), with the largest exhibiting an apparent 2:1 stoichiometry relative to the other two. Visible spectra in the region of 390 to 630 nm do not show any detectable difference from that of the parent cytochrome oxidase, while its heme a and copper content are raised to values around 20 nmol or ng atoms/mg of protein, respectively, corresponding to minimal molecular weights of 50 X 10(3). The molecular weight determined by physical means equals 107 X 10(3). Thus the enzyme probably contains two copies of each subunit. After extensive dialysis to remove as much as possible of the sodium dodecyl sulfate used in its preparation, this enzyme remains in solution in phosphate buffer in the absence of any added detergent, while under similar conditions the seven-subunit complex precipitates completely. A similar preparation can also be obtained from beef heart. The significance of these findings is discussed with respect to the role of the large subunits in the function as well as the biogenesis of the mitochondrial cytochrome oxidase complex.