title: Characterization of NAADP(+) binding in sea urchin eggs.
abstract: Nicotinic acid adenine dinucleotide phosphate (NAADP(+)) is a pyridine nucleotide which has been shown to release Ca(2+) from intracellular membranes in echinoderms, Ascidiae, mammals, and plants. NAADP releases Ca(2+) via a mechanism independent of ryanodine and inositol 1,4,5-trisphosphate (IP(3)) receptors and the NAADP(+) receptor is likely to be located on a separate organelle. We have investigated the binding characteristics of NAADP(+) to its receptor in sea urchin egg homogenates. NAADP(+) binds to a saturable membrane-bound site with high affinity (K(d) = 193 +/- 35. 7 pM). NAADP(+) associates to its receptor with a t(1/2) of approximately 7 min while dissociation does not occur during the time course of the experiment. Furthermore, NAD(+), NAAD(+), ADP, or ATP cannot displace NAADP(+) binding. The structurally related molecules NADP(+) and NADPH displayed a markedly lower affinity for the binding site with K(d)'s 500- and 25,000-fold higher than NAADP(+), respectively. This discrepancy between oxidized and reduced forms of NADP(+) might suggest that NAADP(+) signaling is itself regulated by the redox state of the cell.
authors.affiliation: Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QJ, United Kingdom.
authors.forename: R A
authors.initials: RA
authors.lastname: Billington
authors.forename: A A
authors.initials: AA
authors.lastname: Genazzani
mesh_terms: D000818:Animals; D015220:Calcium Channels / Q000378:metabolism; D053496:Inositol 1,4,5-Trisphosphate Receptors; D009249:NADP / Q000031:analogs & derivatives* / Q000378:metabolism; D010063:Ovum / Q000378:metabolism*; D011485:Protein Binding; D011869:Radioligand Assay; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012617:Sea Urchins
chemical_list: D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D019837:Ryanodine Receptor Calcium Release Channel; D009249:NADP; C024376:NAADP