Synthesis of rat liver microsomal cytochrome b5 by free ribosomes.

Abstract

Free and membrane-bound polyribosomes were separated from liver homogenates and characterized by EM. Using the wheat germ cell-free translation system, total translation products of poly A+RNA extracted from free polyribosomes (poly A+RNAf) showed some correlation to total liver cytosol proteins. Translation products of poly A+RNA from membrane-bound polyribosomes (poly A+RNAmb) showed some similarity to rat serum. Antibody to purified rat serum albumin immunoprecipitated from only the translation products of poly A+RNAmb a single polypeptide of MW 68,000., i.e., 3,000 greater than secreted serum albumin. Antibody to detergent-extracted cytochrome b5 immunoprecipitated from only the translation products of poly A+RNAf a single polypeptide of MW 17,500, identical to that of microsomal cytochrome b5. A consideration of the known properties of cytochrome b5 is consistent with an exclusive site of synthesis on free ribosomes.