[Differences in the cytotoxicity mechanisms of pancreatic and microbial ribonucleases]

The effect of pancreatic and microbial ribonucleases (RNAses) on incorporation of labeled precursors, i. e. 14C-uridine, 14C-thymidine and 14C-glycine into the biopolymers of transplantable cell cultures, as well as their effect on radioactivity of the acid insoluble fraction of the cells labeled with 14C-orotic acid was studied. It was shown that the pancreatic RNAses and RNAses of Streptomyces rimosus in a dose of 1 ED50 determined by the index of the cell monolayer intactness inhibited incorporation of the labeled precursors. The inhibition was rather deep and almost equal. The enzymes lowered also radioactivity of the cells labeled with 14C-orotic acid in proportion to the time of the cell incubation in the presence of the enzymes. On the contrary, RNAses of Bacillus sp. used in analogous doses was significantly less intensive in inhibition of the precursor incorporation and almost did not lower radioactivity of the acid insoluble fraction of the cells totally labeled with 14C-orotic acid.