Inhibition of lactate dehydrogenase activity by polymeric NAD derivatives with different NAD densities

Polymeric NAD derivatives with different NAD densities were prepared by the copolymerization of NAD N6-[N-(N-acryloyl-1-methoxycarbonyl-5-aminopentyl)-propionamide] with acrylamide in different molar ratios, from 4 x 10(-4) to 1 x 10(-2). The cofactor activities of the polymeric NAD derivatives for lactate, yeast alcohol and horse liver alcohol dehydrogenases decreased with the increase in the NAD density of the polymer, and the lactate dehydrogenase showed no activity for the polymeric NAD derivatives with NAD densities of 2 x 10(-3) and 1 x 10(-2) mol/mol acrylamide polymerized. The polymeric NAD derivatives inhibited the activities of lactate and yeast alcohol dehydrogenases but did not inhibit those of horse liver alcohol and malate dehydrogenases. The polymeric NAD derivatives were competitive inhibitors with respect to NAD for the reaction of lactate dehydrogenase: the inhibition constant decreased from 2.2 microM to 0.02 microM with the increase in the NAD density from 4 x 10(-4) to 1 x 10(-2) mol/mol acrylamide polymerized.