Synthesis of [³²P]NAADP for the radioreceptor binding assay

Nicotinic acid adenine dinucleotide phosphate (NAADP) is a major messenger for Ca(2+) mobilization in cells. NAADP-binding proteins are highly selective and have a strong affinity for NAADP. This is the basis of the radioreceptor binding assay, which is used to measure NAADP levels in cells and tissues and to identify cellular stimuli that use NAADP as an intracellular messenger. In the radioreceptor binding assay, radiolabeled NAADP ([(32)P]NAADP) competes with endogenous NAADP present in samples for binding to their receptors. Here, we describe the synthesis of [(32)P]NAADP for use in the radioreceptor binding assay.