Nicotinic acid adenine dinucleotide phosphate (NAADP)-mediated calcium signaling

Nicotinic acid adenine dinucleotide phosphate ( NAADP)(2) is a metabolite of NADP that was first identified as the most potent Ca2+ stores mobilizing molecule in sea urchin egg homogenates more than a decade ago ( 1, 2). It has since been shown to be effective in a wide variety of cells, from plant to animal, including human ( reviewed in Refs. 3 - 5). Its mechanism of action is distinct from those of cyclic ADP- ribose ( cADPR) and inositol trisphosphate ( IP3), and the stores it targets are separate as well ( reviewed in Ref. 6). Recent evidence establishes that NAADP fulfills the criteria of being a second messenger for mobilizing Ca2+ stores ( reviewed in Ref. 7). This article reviews the structure, functions, and the enzymatic synthesis of this new addition to the list of Ca2+ messengers.