Purification and characterization of two ribonucleases from human erythrocytes: immunological and enzymological comparison with ribonucleases from human urine.

Two ribonucleases (RNases), one active against RNA as well as poly(C) and the other more markedly against poly(C), were isolated from human erythrocytes by acetone fractionation in the presence of 0.25 M H2SO4, followed by a series of column chromatographies. The purified enzymes appeared homogeneous as judged by sodium dodecyl sulfate--polyacrylamide gel electrophoresis (SDS-PAGE), and were tentatively designated RNase HE-1 and RNase HE-2. The content of RNase HE-1 in erythrocytes was much higher than that of RNase HE-2. The molecular mass of RNase HE-1 was determined to be 18,000 and 16,000 Da, and that of RNase He-2 39,000 and 31,000 Da, by SDS-PAGE and gel filtration, respectively. The catalytic properties and structural features of RNase HE-1 including the amino acid composition and N-terminal amino acid sequence indicated that its protein moiety is strictly related to a nonsecretory RNase purified from human urine (Yasuda et al., 1988, Biochim. Biophys. Acta 965, 185-195). In particular, the N-terminal amino acid sequence up to the 32nd residue was identical with that of urine nonsecretory RNase reported recently (Beintema et al., 1988, Biochemistry 27, 4530-4538). Furthermore, RNase HE-1 was immunologically indistinguishable from urine nonsecretory RNase, but clearly differed from urine secretory RNase. On the other hand, erythrocyte RNase HE-2 was enzymologically and immunologically similar to urine secretory RNase.