On the molecular weight of mitochondrially synthesized subunits of rat liver cytochrome oxidase.

The subunit composition of cytochrome c oxidase from rat liver mitochondria was studied by dodecylsulfate polyacrylamide gel electrophoresis. The apparent molecular weight of the seven subunits are in reasonable agreement with published data on cytochrome c oxidase subunits from other sources. Two additional subunits were found if the electrophoresis was performed with 8m urea, due to splitting of the smallest subunit. Performic acid oxidation of the isolated subunits I and II increased the apparent molecular weights from 38000 to 48000 and from 24500 to 29000, respectively, accompained by a normalization of the anomalous behaviour of subunit I in the Ferguson plot. It is suggested that performic acid, by splitting extremely inaccessible disulfide bridges, mediates full complexing of the subunits by dodecylsulfate, thus permitting the determination of the real molecular weights by dodecylsulfate polyacrylamide gel electrophoresis.