Guinea-pig pancreatic ribonucleases. Isolation, properties, primary structure and glycosidation

Two ribonucleases were isolated from guinea-pig pancreas by extraction with 0.125 M sulfuric acid, precipitation with acetone and chromatography on carboxymethyl-cellulose. The amino acid sequences were determined from tryptic digests of the aminoethylated proteins. The tryptic peptides were positioned in the sequence by homology with other pancreatic ribonucleases. Both ribonucleases not only differ in the presence (ribonuclease B) or absence of carbohydrate (ribonuclease A), but also at 31 positions of the amino acid sequence. In guinea-pig ribonuclease B a leucine/proline heterogeneity was found at position 64. The carbohydrate in guinea-pig ribonuclease B is attached to asparagine residues at positions 21 and 34. The carbohydrate-free guinea-pig ribonuclease A possesses a recognition site for sugar attachment in the sequence Asn-Val-Ser (62-64).