2 DISTINCT SECRETORY RIBONUCLEASES FROM HUMAN CEREBRUM - PURIFICATION, CHARACTERIZATION AND RELATIONSHIPS TO OTHER RIBONUCLEASES

Two RNAases from human cerebrum were purified to an electrophoreticall y homogeneous state and their molecular masses were 22.0 kDa (tentativ ely called RNAase HB-1) and 19.0 kDa (RNAase HB-2). Analyses of the am ino acid compositions, N-terminal amino acid sequences and catalytic p roperties of these enzymes provided strong evidence that they were str ictly related to the secretory (sec) RNAases, such as the pancreatic e nzyme, very similar immunologically to urinary sec RNAase, but clearly distinguishable from urinary non-secretory (nonsec) RNAase. There wer e several differences between HB-1 and HB-2, namely their immunologica l reactivities with specific antibodies, heat-stabilities, attached ca rbohydrate moieties and molecular masses. In particular, HB-2 appeared to be nonglycosylated, in view of its lack of affinity for several co njugated lectins, the absence of hexosamine and no change in electroph oretic mobility before and after peptide:N-glycosidase F digestion, wh ereas HB-1 and human sec RNAases purified from kidney, pancreas and ur ine all appeared to be glycosylated, as they moved to the same positio n as HB-2 when electrophoresed after glycosidase digestion. An antibod y against urinary sec RNAase inhibited 75 % and 20 % of the total acti vity of the crude cerebral extract against RNA at pH 8.0 and 6.0 respe ctively, whereas an antibody against urinary nonsec RNAase had no such inhibitory effect. These findings suggest that yet another type(s) of cerebral RNAase, which is unable to cross-react immunologically with sec and nonsec RNAases, may exist. Two RNAases corresponding to HB-1 a nd HB-2 were identified in fresh cerebrospinal fluid.