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

3-Chloroacetylpyridine--adenine dinucleotide phosphate is both active as a hydride acceptor and inactivates estradiol 17 beta-dehydrogenase. This coenzyme analogue behaves like an affinity label. The inactivation kinetics are discussed in relation to those observed with 3-chloroacetylpyridine--adenine dinucleotide. The pH dependence of the rate of inactivation, in combination with determination of the number of reactive cysteine residues, pointed to the alkylation of one cysteine residue/subunit. The stoichiometry was one molecule of dinucleotide per subunit and no cooperativity was detected. When 14C-labeled dinucleotide was used, the 14C label was found mainly in one peptide, accounting for 90% of the incorporated radioactivity, whereas in previous work it had been shown that 3-chloroacetylpyridine--adenine dinucleotide is an affinity reagent which labels three peptides.