Research on the carbohydrate-peptide linkage of whale pancreatic ribonuclease W2

The amino acid sequence of pike-whale (lesser-rorqual) pancreatic ribonuclease

Pancreatic RNAase (ribonuclease) from the pike whale (lesser rorqual, Balaenoptera acutorostrata) was isolated by affinity chromatography. The protein was digested with different proteolytic enzymes. Peptides were isolated by gel filtration, preparative high-voltage paper electrophoresis and paper chromatography. The amino acid sequence of peptides was determined by the dansyl-Edman method. Although we do not have an amino acid composition for the whole protein, all peptide bonds were overlapped by one or more peptides. Residues 85-96 are bridged by a peptide of unstaisfactory composition and the sequence here depends, at least in part, on homology for its confirmation. Another region in which a similar situation obtains is residues 39-40. This pancreatic RNAase differs at 24-33% of the positions from all other mammalian pancreatic RNAases sequenced to date, except for pig RNAase, from which it differs by 19%. This indicates that whale RNAase has evolved independently during the larger part of the evolution of the mammals. Lesser-rorqual pancreatic RNAase is partially glycosidated (30%) at asparagine-76 in an Asn-Ser-Thr sequence (residues 76-78). Pig RNAase also has carbohydrate attached to asparagine-76 and is identical with lesser-rorqual RNAase in residues 76-98. Detailed evidence for the sequence has been deposited as Supplementary Publication SUP 50066 (11 pages) at the British Library Lending Division, Boston Spa, Wetherby, W. Yorkshire LS23 7BQ, U.K., from whom copies may be obtained on the terms ginen in Biochem. J. (1976) 135, 5.

Carbohydrate in pancreatic ribonucleases

A survey of the presence and compositions of carbohydrate chains attached to pancreatic ribonucleases is given. Carbohydrate chains may occur at asparagine residues in Asn-X-Ser/Thr sequences at four exposed sites of the molecule (positions 21, 34, 62 and 76). These sites form part of highly variant sequences in pancreatic ribonucleases with the consequence that the enzymes from very closely related species may differ in the presence or absence of carbohydrate. In a number of ribonucleases Asn-X-Ser/Thr sequences occur which carry carbohydrate in only a part of the molecules. The occurrence of Asn-X-Ser/Thr sequences entirely without any carbohydrate also has been demonstrated. Compositions of the carbohydrate moieties of ribonucleases from cow, sheep, pig, whales, giraffe, okapi, moose, horse, coypu, chinchilla, and guinea-pig are presented. Striking differences in complexity have been found, both between chains attached to the same site in different species (cow and giraffe), between chains attached to different sites of the same enzyme in one-species (pig) and even between chains attached to the same site in a single species (chinchilla).