The intracellular inactivation of catalase—II. Characteristics of a cytosol inhibitor in mouse liver

Abstract

1. 1. The hydrolytic cleavage of purified mouse liver catalase by a number of proteinases has been shown to be subject to inhibition by a liver cytosol fraction. 2. 2. It has also been demonstrated that the inhibitory function afforded by the liver cytosol is a characteristic of the tissue per se, and not due to contamination by blood proteinase inhibitors. 3. 3. Of the hydrolytic enzymes tested, inhibition is most apparent against the trypsin-like proteinases; however, liver cytosol has little inhibitory capacity against tryptic hydrolysis of the synthetic trypsin substrate, benzoyl arginine—para—nitroanilide hydrochloride. 4. 4. Inhibition of proteolysis was not specific for catalase as substrate. Pyruvate kinase, for example, was protected to a similar extent against tryptic digestion in the presence of mouse liver cytosol, and other enzymes were also afforded a degree of protection. 5. 5. Investigation of the characteristics of the liver cytosol inhibitor indicated that the factor is evidently a high molecular weight protein or protein aggregate. 6. 6. The significance of these data has been discussed in terms of the regulatory process involved in the degradative processes of catalase and other enzymes.