Immunological studies of ribonuclease C from human urine

Antiserum to human urinary RNase C [ribonuclease (pancreatic), EC 3.1.27.5], developed in rabbits, was used to characterize this enzyme through studies of inhibition of RNase C-catalyzed poly(C) hydrolysis and of competition in a RIA. By either assay, the antiserum failed to cross react with human urinary RNase U (EC 3.1.27.-) or bovine pancreatic RNase A (EC 3.1.27.5). RNase C is immunologically identical to the poly(C)-active RNase in various human sera, including samples obtained from normal individuals, patients with pancreatic carcinoma, pancreatitis, or other malignant and nonmalignant diseases. This conclusion is based on the finding of superimposable antibody dose-inhibition curves for poly(C) hydrolysis and parallel competition RIA curves for RNase C and the various sera. There was a positive correlation (r = 0.73; p less than 0.001) between concentrations of RNase C as determined by poly(C) hydrolysis and competition RIA in serum samples from 102 patients. Therefore, the latter technique provides al alternative method for measuring RNase C in sera.