title: Synthesis of rat liver microsomal cytochrome b5 by free ribosomes.
abstract: Free and membrane-bound polyribosomes were separated from liver homogenates and characterized by electron microscopy. 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. In contrast, 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 mol wt 68,000. i.e., 3,000 greater than secreted serum albumin. In contrast, antibody to detergent-extracted cytochrome b5 immunoprecipitated from only the translation products of poly A+RNAf a single polypeptide of mol wt 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.
mesh_terms: D000418:Albumins / Q000096:biosynthesis; D000818:Animals; D002458:Cell Fractionation; D003580:Cytochromes; D015786:Cytochromes b5; D008862:Microsomes, Liver; D008970:Molecular Weight; D011132:Polyribosomes / Q000378:metabolism*; D014176:Protein Biosynthesis; D012313:RNA / Q000378:metabolism; D051381:Rats
chemical_list: D000418:Albumins; D003580:Cytochromes; D012313:RNA; D015786:Cytochromes b5