Purification and some kinetic parameters of NAD glycohydrolase from Penicillium brevicompactum NRC 829

The current work reports the purification and characterization of some kinetic properties of nicotinamide adenine dinucleotide glycohydrolase (NADase) from Penicillium brevicompactum NRC 829. The enzyme was purified about 286 fold with a specific activity of 400 U/mg protein through a 3-step purification procedure. The purified NADase was shown to have a relative low molecular mass of 48 kDa by sodium dodecyl sulphate poly-acrylamide gel electrophoresis (SDS-PAGE). Nicotinamide and adenosine diphosphoribose (ADP-ribose) were the sole products formed when the purified NADase was incubated with NAD. This result was confirmed by Thin Layer Chromatography (TLC) analysis. The enzyme exhibited a broad pH profile with optimum pH for hydrolysis at 6.0. In addition to NAD and NADP, a number of NAD analogs were shown to serve as substrates for that enzyme. The Kinetic studies using NAD as a substrate followed Michaelis-menten type with 5.1 x 10 M of Km indicates the high substrate affinity of NADase. Product inhibition studies demonstrated nicotinamide to be a noncompetitive inhibitor which has a Ki of 2 x 10 -2 M, while ADP-ribose was found to be a competitive inhibitor with a Ki of 3.6 x 10 -2 M.