Canine Pancreatic Ribosomes II. THE PROTEIN MOIETY

Abstract The protein moiety of purified dog pancreatic ribosomes has been examined by starch gel electrophoresis in formate buffers, pH 3, containing 6 m urea. Densitometric tracings of the complex but reproducible electrophoretograms disclosed a minimum of 21 cationic components. Identical patterns were obtained with protein prepared by alternative extraction procedures, and these were not significantly altered by preparation of the ribosomes from a single dog pancreas or by the inclusion of puromycin during isolation of the ribosomes. Treatment of the protein from canine pancreatic ribosomes with dithiothreitol in urea resulted in very minor changes in electrophoretic properties, the suggestion being that most of the half-cystine residues of the protein are already in the reduced state. Protein from microsomal and postmicrosomal canine pancreatic ribosomes presented similar but not identical patterns. Electrophoretograms of protein moieties of purified ribosomes from dog and rabbit pancreas were compared. Most components were common to both species, but a few were characteristic of one species only. The species-specific bands are reproducible and independent of the method of preparation of the protein. Of the protein present in the 80 S monoribosome of dog pancreas, three components are localized exclusively or predominately in the large subunit, and five exclusively or predominately in the small subunit. One disappears upon dissociation and the remainder appear to be common to both subunits. Of the dog-specific bands, one appears only in the small subunit, one appears only in the large subunit, and one is present in both subunits.