Interaction between dehydrogenases and a new NAD -isomer.

A new NAD -isomer was prepared, in which the D-ribose of the adenosine moiety was substituted by the enantiomeric L-ribose. As compared to nicotinamide-adenine-dinucleotide (NAD) and NADH the coenzyme isomer (D,L)-NAD and its dihydroform (D,L)-NADH are far less tightly bound to lactate dehydrogenase and alcohol dehydrogenase from horse liver. In the presence of the second substrate (D,L)-NAD and (D,L)-NADH act as hydrogen acceptor and hydrogen donator, respectively, with lactate dehydrogenase and alcohol dehydrogenases from horse liver and yeast. Compared to NAD and NADH the Michaelis constants are always increased, the catalytic constants (V/Et) were found to be decreased except for the dihydroform reacting with alcohol dehydrogenase from liver.