Characterization of two High Molecular Weight Proteins Immunoprecipitated with an Antibody against Rat Liver CytochromecOxidase

Abstract

Isolated rat hepatocytes were labeled with [35S]methionine, dissolved in Triton X-100-containing buffer and incubated with antibodies against rat liver cytochrome c oxidase. After separation by dodecyl sulfate-gel electrophroesis the fluorogram of immunoprecipitated proteins showed 2 labeled bands with apparent MW of 52,000 and 182,000. The immunological relationship of the 2 proteins to cytochrome c oxidase was demonstrated by immunocompetition with the isolated enzyme and with purified subunits IV-VIII. Although the precursor nature of the 2 described proteins for cytoplasmically synthesized subunits of cytochrome c oxidase cannot be excluded, the following observations do not support this assumption: the amount of incorporated radioactivity is too high; they are exclusively located within the microsomal fraction; and the turnover is rather slow, compared to that of known precursor proteins.