Comparative Study on the Ribonucleases Isolated from the Debris and Ribosome Fraction of Escherichia coli

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Abstract
A ribonuclease [EC 2.7.7.17] involved in some unknown manner in the debris fraction of Escherichia coli strain B was purified 12, 500 fold by treatment with 4 M urea and 0.05 M NaCl, ammonium sulfate frac-tionation at pH 4.5 and chromatography on CG-50 resin. Its properties and mode of action were studied in comparison with those of latent ribosomal ribonuclease purified 700 fold by the same procedures. The ribonuclease from the debris was adsorbed on a CG-50 column and eluted with 0.2 M potassium phosphate buffer, pH 7.4, containing 0.4 M sodium chloride. It was found that the enzyme has the same catalytic action as ribosomal ribonuclease. However, distinct differences between debris and ribosomal ribonuclease were found in their selectivity to hydrolyze substrate RNA's. The debris ribonuclease acted preferentially on small molecules of ribonucleic acid, while the ribosomal ribonuclease preferentially hydrolyzed ribonucleic acid molecules of high molecular weight. The debris ribonuclease was more heat-stable than the ribosomal ribonuclease. However, both enzymes were inhibited by urea and activated by sodium chloride and they had the same optimal pH range of 7.4 to 7.8. It was suggested that the debris ribonuclease may form a lyso-zyme sensitive complex with components of the cell membrane. The possible mechanism of location of ribonuclease is discussed on the basis of the results.