A PANCREATIC RIBONUCLEASE ACTIVE AT pH 4.5

This is the authors' abstract. We don't add key points for this paper.

When a homogenate of beef pancreas prepared at neutral pH is assayed for RNase activities at pH 4.5 and at pH 7.5, the specific activity at the acid pH is more than half that at neutral pH. Yet the procedures normally employed for the isolation of the well‐characterized RNase A from the pancreas yield an enzyme that is almost devoid of activity at pH 4.5. Experiments designed to isolate from the pancreas the protein responsible for the RNase activity at acid pH have utilized chromatography and gel filtration under conditions that avoid both the strong acidification and the heat which are common features of the methods for the preparation of RNase A. The purified protein active at pH 4.5 (yield, 10 mg per 100 g of tissue) is also active at pH 7.5. The protein is labile to both strong acid and high temperature and it is this sensitivity that has contributed to its being overlooked during the decades when RNase A has been so thoroughly studied. Acid or heat treatment converts the enzyme active at pH 4.5 to a protein which is currently indistinguishable from RNase A, with as yet no detectable change in amino acid composition. Further research is required to define the small but significant chemical or physical changes which accompany this transformation.