SH-CONTAINING COMPOUNDS AS ALLOSTERIC EFFECTORS OF GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE

The rate of hydrolysis of 3-phosphoglyceroyl-holoenzyme, a covalent intermediate of glyceraldehyde-3-phosphate dehydrogenase catalyzed reaction, is considerably decreased in the presence of micromolar concentrations of reduced glutathione, cysteine or dithiothreitol with K(i) values of 0.78 muM, 0.6 muM and 10 muM, respectively. The maximal effect is achieved at a molar ratio [effector]/[tetrameric enzyme] close to unity, which points to subunit cooperativity involved in the stabilization of the covalent intermediate against hydrolysis. The effect is specific for acylholoenzyme conformation and insignificant in the case of hydrolysis of acylated apoenzyme species. The ability of the effectors to stabilize the reaction intermediate against spontaneous hydrolysis, in which water replaces inorganic phosphate as the acyl group acceptor, may be a factor contributing to the specificity and effectiveness of the enzyme catalysis.