Nature and possible origin of Human Serum ribonuclease

Human Serum contains an acidic RNase which is glycoprotein in nature. It is thermostable at pH 4.2 and thermolabile at pH 8.5. It has a pH optimum at 6.5. Its activity either on poly (C) or RNA is endonucleolytic and is absolutely dependent on citrate or phosphate. It exhibits highest preference for the secondary phosphate esters of cytidine 3′-phosphates. It has no action on cytidine 2′:3′-cyclic phosphate. Poly (A) and poly (G) are not only refractory to its action, but also inhibit its action on poly (C). Its rate of hydrolysis of Poly (U) is about 2% of that of poly (C). It differs from bovine pancreatic RNase. It is, however, similar to human pancreatic RNase suggesting that its primary source is pancreas.