Molecular Evolution of Mammalian Pancreatic Ribonucleases

Abstract

Pancreatic ribonucleases form a group of homologous proteins found in considerable quantities in the pancreas of a number of mammalian taxa and a few reptiles (Barnard, 1969; Beintema et al., 1973). The ribonuclease activity varies greatly in different species. Large quantities are found in ruminants and species that have a ruminant-like digestion, and in a number of species with cecal digestion. Barnard (1969) proposed that an elevated level of pancreatic ribonuclease is the response to the necessity of digesting large amounts of ribonucleic acid derived from the microflora of the stomach of ruminants. As rumination and ruminant-like digestion have evolved several times independently during the evolution of mammals (Moir, 1968), pancreatic ribonucleases may show different solutions to the same evolutionary pressure.