Ribonuclease from<em> Alcaligenes eutrophus</em>: Activation by heat treatment, partial purification and some properties.

Heat treatment (10 min at 65&deg; C) of cells of Alcaligenes eutrophus, which resulted in the release of RNA degradadation products into the medium, was found to activate cellular ribonucleases. Two ribonucleases degrading yeast RNA were found, one localized in the periplasmic space and the other in the soluble fraction of the ribosomes. Compared to non-heated cells, in the heat-treated cells the former enzyme, the cell debris ribonuclease, was present at an eightfold increased specific activity, and the latter, the cytoplasmic ribonuclease, was present at a fourfold increased specific activity. This increase was due to the inactivation of a thermolabile inhibitor and to denaturation of part of the soluble protein during heat treatment. With respect to their properties the enzymes were similar; they had endonuclease activity and hydrolysed only RNA. They were heat-stable, resistent to trypsin, highly sensitive to a ribonuclease inhibitor isolated from the same bacterium and were partially inhibited by ATP and GTP. These properties provided a partial explanation for the mechanism of the release of RNA dagradation products from A. eutrophus cells after heat treatment