Unusual (zig-zag) temperature dependence of the rate constant for irreversible thermoinactivation of hydrophilized enzymes

Abstract

Hydrophilized preparations of α-chymotrypsin and trypsin obtained by covalent modification of the enzymes with anhydrides of aromatic carboxylic acids (trimellitic, pyromellitic and mellitic) or with glyoxylic acid display an unusual temperature dependence of the rate constants of irreversible thermoinactivation: the linear plots (with positive and negative values of an effective activation energy) alternate in a zig-zag manner. A formal kinetic scheme describing this behaviour is suggested, involving the temperature-dependent conformational transition of modified α-chymotrypsin into a more stable conformation.