ABSTRACT
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.
Subject(s)
Endoribonucleases , Ribonucleases/urine , Antigen-Antibody Complex , Cross Reactions , Female , Humans , Immune Sera , Kinetics , Male , Radioimmunoassay/methods , Ribonucleases/immunologyABSTRACT
The two major ribonuclease (EC 3.1.27.5) present in normal human urine have been highly purified and extensively characterized for their enzymatic, physical, chemical and structural properties. One of the enzymes, RNAase C, is a glycoprotein which exhibits a pH optimum of 8.5 with RNA as the substrate and preferentially degrades the synthetic homoribopolymer poly(C). This enzyme is resolved into multiple components by column electrofocusing. However, prior treatment with neuraminidase results in a single form of RNAase C with an isoelectric point of 10.4, indicating that the charge heterogeneity is the result of variability in sialic acid content. Amino acid composition and NH2- and COOH-terminal sequence analyses of RNAase C show that this enzyme is very similar to mammalian pancreatic RNAases; the data indicate a peptide chain of 126 amino acid residues and a 33% carbohydrate content. The second enzyme isolated from urine, termed RNAase U, is also a glycoprotein which has a pH optimum of 7.0 with RNA as substrate and is virtually inactive against poly(C). RNAase U lacks sialic acid and focuses as a single component with a highly basic isoelectric point of greater than pH 11.0. The NH2- and COOH-terminal sequences of RNAase U show little homology with the pancreatic RNAases. However, the amino acid composition of this enzyme indicates it is very similar to human spleen RNAase.
