Kinetic Studies on Decomposition of Glutathione. I. Decomposition in Solid State

Abstract

The decomposition of crystalline glutathione (GSH) by water vapour was studied kinetically. The decomposition time course of GSH polymorphs (α and β forms) showed the pattern like autocatalytic reaction in a solid state. The logarithmic plots of the decomposed ratio vs. the reaction time were almost linear for the β form, but broken to two lines for the α form. Decomposition of the α form was more rapid than the β form under the same condition of temperature and humidity. The effect of oxygen in air on the rate was almost negligible. The reaction rate in the early stage of the decomposition was concluded to be larger than the rate calculated from the reaction model in which GSH decomposed in the saturated solution on the crystal surface. The rates were apparently proportional to about 3 to 5 powers of humidity. γ-Glutamyl bond was broken and some parts of products underwent intramolecular condensation in the decomposition. A small amount of oxidized GSH was formed but the decreased ratio of reductivity of the sample was considerable and increased with increasing decomposition ratio of GSH. Apparent activation energy for decomposition of both forms was 32 to 33 kcal/mol.