CD38 in Bovine Lung: A Multicatalytic NADase

We report the kinetics and molecular properties of CD38 purified from bovine lung microsomal membranes after its solubilization with Triton X-100. The enzyme was found to be a novel member of a multicatalytic NAD⁺-glycohydrolase (NADase, EC 3.2.2.6). It was able to utilize NAD ⁺ in different ways, producing nicotinamide (Nam) and either adenosine diphosphoribose (ADPR, NADase activity) or cyclic ADPR (cADPR, cyclase activity); it also catalyzed the hydrolysis of cADPR to ADPR (cADPR, hydrolase activity). In addition, the enzyme catalyzed the pyridine base exchange reaction with conversion of NAD ⁺ into NAD analogues. These data are evidence that CD38 is involved in the regulation of both NAD⁺ and calcium-mobilizing agents, the concentration resulting in an essential enzyme that plays a key role in cellular energy and signal-transduction systems.