Canine Pancreatic Ribosomes

Purified microsomal and postmicrosomal ribosomes have been prepared from dog pancreas by a method involving magnesium precipitation and treatment with sodium deoxycholate. The purified ribosomes were shown to be substantially free from contamination with supematant protein in an experiment employing a radioactive supematant fraction. They contain less than 0.1% of digestive enzymes known to be major products of synthesis by the gland. The purified particles appear to contain 60% RNA when pancreatic ribosomal protein is used as the protein standard in the Lowry procedure. Different values are obtained, however, when either bovine serum albumin or bovine pancreatic chymotrypsinogen is used as standard. The monoribosome behaves ultracentrifugally as an 80 S species in the presence of 0.1 M KC1 and as a 74 S species in its absence. Lyophilization causes partial dissociation of the monoribosome to ribosomal subunits, complete dissociation being effected by ethylenediaminetetraacetate at a concentration of 2 pmoles per mg of ribosome. The large and small subunits sediment, respectively, as 50 S and 33 S species in the presence of 0.1 M KC1 and as 34 S and 29 S species in the absence of KCl. The individual subunits have been isolated by density gradient centrifugation, and their chemical composition has been studied.