Effect of Sulphydryl Reactants on Liver Ribonuclease

Abstract

WHILE investigating the characteristics of rat liver ribonuclease it was noted that several reagents which react with sulphydryl groups increased the activity of this enzyme in homogenates. 4 × 10⁻⁴ M silver or lead ions increased the activity approximately 25 per cent, while saturation of the test system with p-chloromercuribenzoic acid or phenyl mercuric chloride caused a similar increase. Cupric ion of 4 × 10⁻⁴ M concentration was, however, inhibitory to the extent of 50 per cent. The inhibitory action of cupric ions could be reversed by the addition of 2,3-dimercaptopropanol (BAL); but this compound had no effect on systems containing the other sulphydryl reacting agents, or on the enzyme alone. The accompanying graph shows the results of a typical experiment.