PURIFICATION AND PROPERTIES OF ALKALINE RIBONUCLEASE FROM HUMAN-SERUM

Five alkaline RNase (EC 3.1.4.22) were purified .apprx. 140- to 1900-fold from human serum by phosphocellulose and DEAE-cellulose chromatographies and Sephadex G-75 filtration, with a total recovery of 22%. These were designated as RNases 1-5. Optimum activities were observed at pH 8.5-8.7 for RNases 1-4, and at pH 7.5 for RNase 5. The molecular weights of these enzymes were estimated by gel filtration as 45,000, 32,000, 20,000, 13,000 and 8500, respectively. These RNases were heat-labile proteins but are markedly stabilized with bovine plasma albumin. The reaction was activated by Na+, K+, Mg2+ and Ca2+, and inhibited by Co2+, Fe2+, Cu2+ and Zn2+. EDTA had little effect on the velocity of the reaction. Spermine caused 2- to 7-fold activation. Among the substrates examined, these RNases preferentially hydrolyzed pyrimidine bodies and except for RNase 5, had a higher affinity for poly(C) than poly(U) as substrate. Each enzyme was free from other nucleolytic enzymes and hydrolyzed only RNA.