Explanation of the observation of pancreatic ribonuclease activity at pH 4.5.

A recent conclusion that beef pancreas contained a molecular species of ribonuclease with intrinsically high activity at pH 4.5 has been found to be incorrect. The particular assay used in the earlier experiments gives anomalous results at acid pH in the presence of low concentrations of ions such as phosphate which was used during the fractionation. By turning to the more widely employed form of the perchloric acid precipitation assay, interference is avoided and the ribonuclease in beef pancreas is confirmed as consisting almost completely of the molecular species well-characterized as ribonuclease A. The clarification of the assay question permits a clear interpretation of the results of each step of the chromatographic purification procedure that led to the initial conclusion, including an artifact that arose when gel filtration was attempted with distilled water rather than with buffer.