Comparison of the properties of ribonucleases in human liver tissue and serum.

Two ribonucleases (RNases) with acidic pH optima were partially purified, one from normal human liver tissue and the other from serum. The properties of the two enzymes were studied and compared. Liver RNase was partially purified about 700-fold by acid fractionation, phosphocellulose column chromatography, Sephadex G-75 gel filtration, and polyguanylate affinity column chromatography. Serum RNase was purified about 1200-fold by phosphocellulose column chromatography and Sephadex G-75 gel filtration. The two RNases showed a similar optimal pH and molecular mass, and similar behaviour towards metal ions, but they differed in their substrate specificity. Liver RNase displayed a higher activity towards polyuridylate (poly(U)) than towards polycytidylate (poly(C)), while serum RNase hydrolysed poly(C) more rapidly than poly(U). These findings suggest that liver RNase is not the primary source of the serum RNase with an acidic pH optimum.