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

The rate of hydrolysis of 3-phosphoglyceroyl-holoenzyme, a covalent in termediate of glyceraldehyde-3-phosphate dehydrogenase catalyzed react ion, is considerably decreased in the presence of micromolar concentra tions of reduced glutathione, cysteine or dithiothreitol with K(i) val ues 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 u nity, which points to subunit cooperativity involved in the stabilizat ion of the covalent intermediate against hydrolysis. The effect is spe cific for acylholoenzyme conformation and insignificant in the case of hydrolysis of acylated apoenzyme species. The ability of the effector s to stabilize the reaction intermediate against spontaneous hydrolysi s, in which water replaces inorganic phosphate as the acyl group accep tor, may be a factor contributing to the specificity and effectiveness of the enzyme catalysis.