DISTRIBUTIONS OF PANCREATIC RIBONUCLEASE CHYMOTRYPSIN AND TRYPSIN IN VERTEBRATES

The distri-bution of pancreatic RNase in 38 species of vertebrates was analyzed. The occurrence of trypsin and chymotrypsin was determined in pancreas from a majority of these species. An RNase of the same type as that produced by the exocrine pancreas of the cow was found in moderate or high levels in all of the species of ungulates examined; particularly high contents exist in the ruminants, and also in the 2 marsupials tested. It is also present in lower but appreciable amounts in some species of whales, turtles, and frogs. It was virtually absent in the rabbit, elephant, dog, cat, and primates; in birds and certain amphibia; and in the elasmobranch and teleost fishes examined. The effects of acid in inactivating some RNases in pancreatic extracts and in releasing others from a bound state are described. Trypsin-like and chymotrypsin-like enzymes were found abundantly in all species investigated. Considerable amounts of other proteases and/or pepti-dases, which have neither tryptic nor chymotryptic activities, are present in many species. This latter protease fraction is resistant to specific irreversible inhibitors of trypsin and chymotrypsin. The contributions of the various proteases to the total caseinolytic activity vary greatly among the species. The proteases in an extract from tuna were partly purified, and were characterized by the use of specific substrates and inhibitors.