COMPARATIVE CHEMICAL MODIFICATION STUDIES OF YEAST AND RABBIT MUSCLE GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASES - STRUCTURE AND CHEMICAL-REACTIVITY RELATIONSHIP

Chemical modification of cysteine 149 residues from yeast apo-glyceraldehyde-3-phosphate dehydrogenase either by iodoacetamidonaphthol or N-(4-dimethylamino-3,5-dinitrophenyl) maleimide results in the disappearance of free SH groups according to all-of-the-sites reactivity, whereas loss of the dehydrogenase activity occurs following half-of-the-sites reactivity. Chemical modification of the same cysteine residues of the rabbit muscle apoenzyme by N-(4-dimethylamino-3,5-dinitrophenyl) maleimide shows that both loss of activity and disappearance of the SH groups may be described as all-of-the-sites reactivity phenomena. After chemical modification by iodoacetamidonaphthol both processes follow half-of-the-sites reactivity. Moreover SH reagents like iodoacetamidonaphthol, iodoamidosalicylic acid and dinitrofluorobenzene which inactivate rabbit muscle apoenzyme according to a half-of-the-sites reactivity induce different conformational changes in the protein. These results underline the structural differences which exist between rabbit muscle and yeast glyceraldehyde-3-phosphate dehydrogenases. They also show that interpretation of a half-of-the-sites reactivity phenomenon observed with one glyceraldehyde-3-phosphate dehydrogenase is not necessarily valid for homologous enzymes of different origins. The same reagent can induce opposite effects depending on the enzyme or the parameter being observed.