Binding of estrogen and progesterone-BSA conjugates to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and the effects of the free steroids on GAPDH enzyme activity: physiological implications

In this study rat brain solubilized plasmalemma-microsomal fractions (B-P3) or cytosolic fractions were applied to P-3-BSA (progesterone linked to BSA at C-3 position) and E-6-BSA (17beta-estradiol linked to BSA at C-6 position) affinity columns. It is interesting that a 37 kDa protein was retained by both columns which was identified as glyceraldehyde-3-phosphate dehydrogenase (GAPDH) by N-terminal sequencing. The 37 kDa protein (GAPDH) was not retained by either a control BSA conjugated affinity column or a corticosterone-BSA affinity column. E-6-BSA bound to GAPDH with higher binding affinity than P-3-BSA or T-3-BSA (testosterone linked to BSA at C-3 position) affinity columns. In addition, the binding of 17beta-E-6-BSA to GAPDH was impeded by free estrogen (17beta-estradiol) completely. Binding studies of E-6-BSA and P-3-BSA to commercial GAPDH from rabbit skeletal muscle using radiolabeled ligand binding assays revealed that P-3-BSA had 10x lower GAPDH binding affinity than E-6-BSA. Next, the effects of estrogen and progesterone on GAPDH activity were studied. Rapid and significant increases in V(max) and changes in K(m) were observed by the addition of 10 nM estradiol, whereas 100 nM progesterone decreased only V(max) significantly. Testosterone, corticosterone, 17alpha-estradiol, and diethylstilbestrol did not affect the enzyme activity. The results indicate that GAPDH is a target site for 17beta-estradiol and progesterone and suggest possible roles in the regulation of cellular metabolism and synaptic remodeling in which GAPDH has been reported to be involved.