Nicotinic acid adenine dinucleotide phosphate analogues containing substituted nicotinic acid: Effect of modification on Ca²⁺ release

Analogues of nicotinic acid adenine dinucleotide phosphate (NAADP) with substitution at either the 4- or the 5-position position of the nicotinic acid moiety have been synthesized from NADP enzymatically using Aplysia californica ADP-ribosyl cyclase or mammalian NAD glycohydrolase. Substitution at the 4-position of the nicotinic acid resulted in the loss of agonist potency for release of Ca²⁺-ions from sea urchin egg homogenates and in potency for competition ligand binding assays using [³²P]NAADP. In contrast, several 5-substituted NAADP derivatives showed high potency for binding and full agonist activity for Ca²⁺ release. 5-Azido-NAADP was shown to release calcium from sea urchin egg homogenates at low concentration and to compete with [³²P]NAADP in a competition ligand binding assay with an IC₅₀ of 18 nM, indicating that this compound might be a potential photoprobe useful for specific labeling and identification of the NAADP receptor.