Cyclic ADP-ribose. A new component of calcium signaling.

Cyclic ADP-ribose is a recently discovered metabolite of NAD that appears to function in cellular calcium signaling. The discovery that NAD glycohydrolases are bifunctional enzymes that catalyze both the synthesis and hydrolysis of cyclic ADP-ribose raises many questions concerning the mechanisms by which these enzymes function in calcium signaling. Likewise, the identification of human lymphocyte antigen CD 38 as a bifunctional NAD glycohydrolase raises interesting questions concerning the involvement of cyclic ADP-ribose mediated calcium signaling in immune function. The dementia associated with niacin deficiency has been a long-standing curiosity. This signaling mechanism may resolve questions connecting this vitamin deficiency to central nervous system (CNS) function.