CD38 is also named as ADP-ribosyl cyclase 1 and belongs to the ADP-ribosyl cyclase family. The CD38 cDNA sequence predicts an unusual 30 kDa polypeptide with a short N-terminal cyto- plasmic tail,and a carboxyl-terminal extracellular domain carrying the four potential N-linked glyco- sylation sites. It usually acts as a 45 kDa bifunctional ectoenzyme that catalyzes the synthesis of cyclic ADP-ribose (cADPR) from NAD1 and the hydrolysis of cADPR to ADP-ribose. It has 2 isoforms produced by alternative splicing.