Primary structures of pancreatic ribonucleases from Bovidae. Impala, Thomson's gazelle, nilgai and water buffalo

Abstract

The amino acid sequences of the pancreatic ribonucleases from impala Thomson's gazelle, nilgai and two types of water buffalo were studied from several enzymic digests. Peptides were positioned by homology with other ribonucleases of known sequence. Only peptides that differ in amino acid composition from the corresponding peptides of ox and goat ribonuclease were sequenced. The primary structures of pancreatic ribonucleases from 11 species of the Bovidae family are known to date. The evolutionary rate of bovid ribonucleases is 2--3 times lower than the average rate observed in all mammals. A possible explanation is that the presence of a stable symbiotic system in the rumen of grass-eating ruminants has caused a slowing down of the evolutionary rate of pancreatic ribonuclease in this taxon. The subfamily of the Bovinae (five species) exhibits a slightly higher evolutionary rate; most replacements in the Bovinae occur near residues 34--36, the most commonly observed carbohydrate attachment site in ribonucleases.