Effect of a modified separation procedure on the size and protein-synthetic activity of membrane-bound liver polyribosomes.
1. Various subcellular fractions containing ribosomes were isolated from rat liver. 2. In the presence of [(14)C]leucine and Sephadex-treated cell sap the radioactivity incorporated into the synthesized protein resulting from the incubation of microsomal preparations or deoxycholate-treated polyribosomes was dependent on the amount of rRNA incubated. In contrast, when Sephadex-treated post-mitochondrial supernatant was incubated, the radioactivity incorporated into the synthesized protein was independent of the amount of rRNA incubated. 3. Microsomal preparations and membrane-bound ribosomes, prepared by the standard procedure, incorporated less [(14)C]leucine into protein, per mg of rRNA incubated, than free or deoxycholate-treated polyribosomes; accordingly, polyribosomes associated with the former fractions were found mainly as monomers. 4. If microsomal fractions or membrane-bound ribosomes were prepared by a simple modification of the standard procedure, i.e. by centrifugation on to a ;cushion' of 2m-sucrose, their protein-synthesizing activity was of the same order as that of the original post-mitochondrial supernatant, and membrane-free and deoxycholate-treated polyribosomes; in this case polyribosome profiles showed that very little degradation had occurred and compared well with those obtained for post-mitochondrial supernatant and isolated polyribosomes. 5. A method is described (Appendix) that provides a rapid and reliable assessment of the concentration of rRNA in subcellular fractions.
D000818:Animals; D001647:Bile Acids and Salts; D002247:Carbon Isotopes; D002458:Cell Fractionation; D066298:In Vitro Techniques; D007930:Leucine / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008297:Male; D008566:Membranes; D008722:Methods; D008862:Microsomes, Liver / Q000378:metabolism; D014176:Protein Biosynthesis; D012313:RNA / Q000032:analysis; D012335:RNA, Ribosomal / Q000378:metabolism; D051381:Rats; D012270:Ribosomes / Q000378:metabolism*; D014461:Ultracentrifugation
D001647:Bile Acids and Salts; D002247:Carbon Isotopes; D012335:RNA, Ribosomal; D012313:RNA; D007930:Leucine