Alkylation of estradiol 17beta-dehydrogenase from human placenta with 3-chloroacetylpyridine--adenine dinucleotide.

3-Chloroacetylpyridine--adenine dinucleotide, which is active as a hydride acceptor (Km = 0.6 mM), inactivates and alkylates estradiol 17beta-dehydrogenase. The kinetics of inactivation by 3-chloroacetylpyridine--adenine dinucleotide and the absence of inactivation by 3-chloroacetylpyridine ribose phosphate show that the alkylation follows the formation of a binary complex (Kd = 4.5 X 10(-4) M). Studies of the labelling by 3-chloro[2-14C]acetylpyridine--adenine dinucleotide and the rate of alkylation as a function of pH, give evidence to the alkylation of a cysteine, the stoichiometry being one mole per subunit. The 14C label is distributed between three chymotryptic peptides, one of which accounts for about 50% of the radioactive label.