The hydrolysis of S-D-lactoylglutathione.

S-o-Lactoylglutathione is a thioester derivative. It is the physiological intermediate of the glyoxalase system and is present in the cytosol of cells and cellular organelles [l]. Exogenous S-o-lactoylglutathione. added to the extracellular medium of human leukaemia 60 cells in culture induces growth arrest and toxicity; the IC,, = 82 wM. There is no similar toxicity in corresponding differentiated cells, neutrophils and red blood cells in culture [2,3]. S D Lactoylglutathione is currently under evaluation as a prospective anti-proliferative, anti-tumour agent. The stability of S-o-lactoylglutathione (and other S-2hydroxyacylglutathiones in stock solutions at ambient and physiological temperature, and at physiological and non-physiological pH may be a limiting factor in their therapeutic application. S-o-Lactoylglutathione and other S-P-hydroxyacylglutathione derivatives hydrolyse spontaneously to reduced glutathione and corresponding aldonic acid: RCH(0H)CO-SG + H,O + RCH(OH)CO,H + GSH. The effect of pH and temperature on the rate of hydrolysis of S-Olactoylgl utathione, and other S(R) -2-hydroxyacyl glutathione derivatives was investigated. Thioester hydrolysis was determined by reaction with 5,5sdithiobis(2-nitrobenzoic acid), DTNB [4]. S-DLactoylglutathione undergoes hydroxide-catalysed hydrolysis. The reaction was first order with respect to hydroxide concentration between pH 7.0 and 9.0, first order with respect to S-o-lactoylglutathione concentration, and independent of phosphate buffer concentration. The rate of reaction -d[SLG]/dt = k.[SLG][OH'], where k = 14.9 f 1.1 M-'s" at 37'C (n = 16). From the Arrhenius plot of the hydrolysis of S-Olactoylglutathione in the temperature rarge 18-37'C, the activation energy AE,, = 81 f 4 kJmol (n = 15). At 37'C, the activation enthalpy AH = 76 f 4 kJmol;' and the activation entropy AS,,, = 4{? f 0.1 JK-hol' .