4,4′-Bis dimethylaminodiphenylcarbinol: A new reagent for selective chemical modification. Interaction with porcine malate dehydrogenase

Abstract

4,4-bis Dimethylaminodiphenylcarbinol (BDC-OH) has recently been reported to be a highly sensitive reagent for the quantitative determination of sulfhydryl residues in biological materials (1). In this communication the effectiveness of BDC-OH as a reagent for selective chemical modification of “active center” cysteine residues was investigated. The supernatant and mitochondrial forms of malate dehydrogenase were chosen for investigation by this reagent. Supernatant malate dehydrogenase which has never been found to contain an “active center” cysteine is unaffected by this reagent. Mitochondrial malate dehydrogenase (L malate: NAD+ oxidoreductase, EC 1.1.1.37) from porcine heart can be irreversibly inactivated by a 20 fold M excess of the reagent. Chemical modification of two essential sulfhydryl residues is prevented by the presence of the coenzyme, NAD+, suggesting that the site of interaction is located at or near the coenzyme binding site and hence at or near the enzymatic center of this enzyme.