Interactions of aldolase and glyceraldehyde-3-phosphate dehydrogenase: molecular mass studies

A gel penetration technique, that measures the dilution undergone by protein equilibrium on a short tightly packed gel column, has been employed to determine the molecular masses of aldolase (160 kDa), glyceraldehyde-3-phosphate dehydrogenase (GPDH; 145 kDa) in the absence and presence of each other and of other proteins. The dilution factor (concentration of protein applied/concentration of protein after equilibration) was found to be inversely related to the molecular mass of the protein. In equimolar mixtures of aldolase and GPDH, 0.5-2.5 microM each, the two enzymes exhibited a common molecular mass value of 309-316 kDa. These enzymes did not undergo any self association or disassociation in this concentration range. Moreover, their molecular masses were unaffected by the presence of other proteins tested. When the concentration of one of these enzymes (aldolase or GPDH) was held constant and that of the other varied, the dilution factor of the former was decreased as the concentration of the latter was increased until it corresponded to a molecular mass of ca. 310 kDa at equimolar concentrations of the two enzymes. Further increase in the concentration of the variable enzyme had no effect. It has been suggested that aldolase and GPDH form a 1:1 complex of dissociation constant equal to or less than 5 x 10(-8) M. The complex was found to dissociate in the presence of KCl, (NH4)2SO4, ATP and NADH whereas its formation was favoured by fructose-1,6-bisphosphate, glyceraldehyde-3-phosphate, NAD+, ADP, AMP and phosphate ions.