NAD(P)+-glycohydrolase from human spleen: a multicatalytic enzyme

NAD(P)(+)-glycohydrolase (NADase, EC 3.2.2.6) was partially purified from microsomal membranes of human spleen after solubilization with Triton X-100. In addition to NAD(+) and NADP(+), the enzyme catalyzed the hydrolysis of several NAD(+) analogues and the pyridine base exchange reaction with conversion of NAD(+) into 3-acetylpyridine adenine dinucleotide. The enzyme also catalyzed the synthesis of cyclic ADP-ribose (cADPR) from NAD(+) and the hydrolysis of cADPR to adenosine diphosphoribose (ADPR). Therefore, this enzyme is a new member of multicatalytic NADases recently identified from mammals, involved in the regulation of intracellular cADPR concentration. Human spleen NADase showed a subunit molecular mass of 45 kDa, a pI of 4.9 and a K-m value for NAD(+) of 26 mu M. High activation of ADPR cyclase activity was observed in the presence of Ag+ ions, corresponding to NADase inhibition.