Interaction of the electrolytically prepared dimers of nicotinamide adenine nucleotide, (NAD)2, and nicotinamide adenine nucleotide phosphate, (NADP)2, with lactate, alcohol, glyceraldehyde 3-phosphate, alpha-glycerophosphate, glutamate and glucose-6-phosphate dehydrogenase has been studied using the quenching of protein fluorescence, kinetics of inhibition and the stopped-flow method. It has been shown that these enzymes are able to bind dimers preserving their coenzyme specificity. The most efficient binding of (NAD)2 has been observed in the case of glutamate and lactate (bovine heart) dehydrogenase, the dissociation constants being 6 and 8 microM, respectively. (NADP)2 affinity to glutamate and glucose-6-phosphate dehydrogenase is also fairly high. More detailed studies on the interactions of dimers with alcohol and glutamate dehydrogenase have shown that the binding to the coenzyme binding site is the prerequisite for the association. However, some additional stabilizing interactions with other enzyme groups are not excluded, though (NAD)2 does not bind to the known binding sites of these enzymes, such as the substrate pocket of alcohol dehydrogenase and the regulatory binding sites for ADP and GTP of glutamate dehydrogenase.