Collect. Czech. Chem. Commun. 1990, 55, 1366-1371

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

Virginius Šikšnisa, Vadim V. Mozhaevb, Nina Galkantaitea, Nikolai S. Melik-Nubarovb, Genadii Denisa and Karel Martinekc

a Research Institute of Applied Enzymology, 232 028 Vilnius, Lithua
b Chemistry Department, Moscow State University, 117 234 Moscow, U.S.S.R.
c Institute of Organic Chemistry and Biochemistry, Czechoslovak Academy of Sciences, 166 10 Prague, Czechoslovakia


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.