Abstract
Cytosolic adenylate kinase (AK1) was eluted with a high yield from an affinity column of blue dextran-Sepharose 4B which bound AK1 with NADH at a low concentration but not with NAD+ at the same concentration. The difference spectrum of AK1-NADH complex against free AK1 and NADH showed positive maxima at 269nm and 273nm and a negative maximum around 326nm, and that of AK1-NAD+ complex also showed a positive maximum at 275nm. NADH and NAD+ competitively inhibited AK1 with respect to both AMP and ATP. From these results and reference data describing on topological equivalence between substrate-binding sites of AK1 and NAD-binding site of dehydrogenases, we can speculate that NAD adenine and nicotinamide moieties bind to ATP and AMP-binding sites of an AK1 molecule, respectively.
