Inhibition of N8-acetylspermidine deacetylase by active-site-directed metal coordinating inhibitors.

A number of substrate analogues of N8-acetylspermidine (N8-AcSpd) (16) and chemical modifying agents containing metal coordinating ligands were assayed as inhibitors of the cytoplasmic enzyme N8-AcSpd deacetylase from rat liver. The enzyme is inhibited by metal chelators, several omega-amino-substituted carboxylic acids, and some thiol reagents. Inhibition by diisopropyl fluorophosphate was observed only at high concentrations. These results suggest that the catalytic mechanism of the enzyme requires a transition state metal and free sulfhydryl groups for activity. The most potent inhibitor synthesized 6-[(3-aminopropyl)amino]-N-hydroxyhexanamide (15), has an apparent Ki of 0.001 microM. It binds to the target enzyme 11,000 times tighter than the substrate (apparent Km = 11 microM). These compounds and a previously reported series of compounds (Dredar, S. A.; Blankenship, J. W.; Marchant, P. E.; Manneh, V. A.; Fries, D. S. J. Med. Chem. 1989, 32, 984-989) are useful in mapping the active site and determining the physiological function of N8-AcSpd deacetylase.