The preparation of stable enzyme-coenzyme complexes with endogenous catalytic activity

N6-(6-Aminohexylcarbamoylmethyl)-NAD+ was coupled to lactate dehydrogenase by using glutaraldehyde to form an active complex. The stability of this complex could be considerably improved by reduction with KBH4, although this treatment caused a partial decrease in specific activity. NAD+ was also coupled directly to the enzyme by this method. All of these complexes exhibited an intrinsic activity in the absence of exogenous NAD+.