KINETIC STUDIES ON THE REACTION BETWEEN THIOL-TYPE THIAMINES AND OXIDIZED EGG ALBUMIN

概要

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1. The formation of protein-thiamine complex (mixed disulfide) in the reaction of iodine-oxidized egg albumin and thiol-type thiamine or O-benzoylthiamine (reaction II) proceeds according to pseudo-first order kinetics in its initial stage where SS groups of the protein is in excess to the thiamine thiol.2. Rate constant is larger in the O-benzoylthiamine reaction than in that of thiamine at each temperature, but the constants are both smaller than that of the reaction between disulfide-type thiamine and SH groups of heat-denatured albumin (reaction I).3. Activation energies for the reactions of thiamine and O-benzoylthiamine with oxidized protein are both about 30 kcal per mole. This shows that the reaction of the type II needs the larger energy than the reaction of type I.4. Applying the absolute reaction rate theory, thermodynamic quantities of the reactions in their activated state were calculated.Entrorpy of activation is negative for reaction II, and positive in reaction I. However, heat of activation and free energy of activation are positive and fairly large in the two reactions, showing the endothermic nature of the reactions. It is further confirmed from these kinetic data that the thiamine-protein complex is formed by the covalent bound through chemical interactions.
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