Polycytidylate hydrolysing ribonuclease activity of human pancreatic secretions

Abstract

Pure human pancreatic juice contains polycytidylate hydrolysing ribonuclease. In 0.05M sodium phosphate buffer and 0.05M sodium phosphate-borate buffer, its pH optimum is at 6.5. In 0.05M Tris-acetate buffer, its pH optimum is at 7.5. Its activity in 0.05M sodium phosphate-borate buffer of pH 6.5 and 0.05M Tris-acetate buffer of pH 7.5 respectively is 86% and 52% of that in 0.05M sodium phosphate buffer of pH 6.5. Thus, sodium phosphate buffer is preferable to other two buffers. However, the concentration of phosphate is critical. For optimal activity the phosphate concentration is 0.05M. Above this concentration, phosphate has a pronounced inhibitory effect. It is inhibited by borate. The presence of phosphate obviates to a great extent the borate inhibition. Polyadenylic and polyguanylic acids are refractory to its action. Its activity on polyuridylic acid is less than 2% of that on polycytidylic acid. Basal duodenal aspirates and those derived after secretin stimulation contain RNase with properties similar to those described above. In basal duodenal aspirates, RNase is not detectable in 7 out of 28 patients. During the first ten minute period after secretin administration, there is a rapid and dramatic increase in the RNase levels of duodenal aspirates. This rapid increase is followed by a decrease and considerable fluctuation in the RNase levels of duodenal aspirates collected during the subsequent periods.