[Physico-chemical properties of terrylytin modified by a copolymer based on vinylpyrrolidone]

The proteolytic activity of terrylytin produced by the culture of Asp. terricola and modified by a water-soluble copolymer of vinylpyrrolidone and acrolein remained unchanged after enzyme modification. Using micro-thin layer chromatography, it was shown that the bulk of the epsilon-amino groups of lysine residues of the protein enter the reaction with the aldehyde groups of the polymeric matrix. The sedimentation and diffusion patterns of the polymerenzyme adduct demonstrated that the molecular weight of the modified enzyme is the total of molecular weights of its constituent components. Evidence from viscosimetry and gel chromatography allowed to develop a hydrodynamic model of the macromolecular product. It was shown that the rate of the enzyme inactivation in the solution calculated from the first order reaction equation depends on the nature of the enzyme electrochemical microenvironment. Under conditions close to physiological ones the rate inactivation constant for terrylytin modified by a neutral polymeric matrix is 10 times less than that for the native enzyme. At the isoelectric point (pH 4,6) a positively charged polymeric form of terrylytin is found to be the most stable one. The pH and temperature optima for casein hydrolysis remained unchanged throughout polymeric modification. The polymeric membrane did not hamper the diffusion during approximation of the substrates (casein and insulin) to the enzyme molecule during the catalytic act, which manifested itself in a constancy of Michaelis curves. Terrylytin modification by a copolymer causes an increase of stability with respect to trypsin proteolysis and a decrease of human blood plasma affinity for the inhibitors. The apparent inhibition constants for modified enzyme forms do not depend on the nature of electrochemical microenvironment and exceed that for native terrylytin 10-fold.