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Trypsin- and thrombin-catalysed hydrolysis of the Nalpha-aryl-sulfonyl-L-arginine methyl esters was studied. Michaelis constants and kcat were determined. The hydrolysis of the substrates by trypsin appears to depend on the polar nature of substitutes. The thrombin- catalysed reaction was believed to be sensitive to steric effects of the introducted groups.

An inverse correlation was observed between the alterations in concentration of free cholesterol and an antioxidative activity of lipids in several tissues and cells. The effect was studied in mice liver tissue on reparative regeneration after partial hepatectomy, in intact mice liver under the directed action on the system of free radical reactions of cell lipid oxidation and in a culture of Hela cells during various periods of cell cycle. Using as a model system the thermal oxidation of oleic acid methyl ester cholesterol was found to function as a substrate in the reactions of free-radical cooxidation and the products of oxidation of cholesterol were active as antioxidants. The significance of a system containing cholesterol and its oxidizing products is discussed in connection with the metabolism of cholesterol itself and in reactions, related to alteration in free-radical oxidation of cell lipids.