ImmunologicalStudieson RibonucleaseC from HumanUrine

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 immu-nologically identical to the poly(C)-active RNase in various human sera, including samples obtained from normal in-dividuals, patients with pancreatic carcinoma, pancreatitis, or other malignant and nonmalignant diseases. This con-clusion 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 <0.00 1) between concentrations of RNase C as determined by poly(C) hydrolysis and competition RIA in serum sample