Affinity labeling of the cofactor-binding site of estradiol 17β-dehydrogenase of human placenta by 5'- p-fluorosulfonylbenzoyl adenosine

Abstract

An analogue of adenosine nucleotide, 5'- p-fluorosulfonylbenzoyl adenosine (5'-FSB-Ado), appears to interact irreversibly with the cofactor-binding site of estradiol 17β-dehydrogenase of human placenta. This conclusion is based on the following observations: (1) The estradiol 17β-dehydrogenase is inhibited by 5'-FSB-Ado. When NAD + is the variable component in the presence of saturated amount of steroid, the type of the inhibition is competitive in nature. When the steroid is the variable component, mode of the inhibition becomes non-competitive. The results suggest reversible binding of 5'-FSB-Ado to the cofactor-binding site of the dehydrogenase. (2) 5'-FSB-Ado inactivates irreversibly the estradiol 17β-dehydrogenase in time- and concentration-dependent manners, following pseudo-first-order kinetics. But, no inactivation is observed in the presence of p-fluorosulfonylbenzoic acid, suggesting that adenosine moiety of 5'-FSB-Ado is essential for the affinity labeling of estradiol 17β-dehydrogenase. (3) NADP + protects completely estradiol 17β-dehydrogenase from the inactivation of 5'-FSB-Ado, whereas NAD(H) is partially protective against the inactivation, suggesting that phosphate moiety at 2'-position of NADP + disturbs the covalent binding of 5'-FSB-Ado at or near the cofactor-binding site of the enzyme. (4) 2',5'-ADP shows the significant protection against the inactivation by 5'-FSB-Ado, but less effect is observed in the presence of nicotinamide mononucleotides. These results suggest that 5'-FSB-Ado is an affinity ligand for binding-site of adenosine nucleotide moiety of the cofactor.