D-myo-inositol-1,4,5-trisphosphate (InsP3) is a putative intracellular second messenger for the mobilization of Ca2- from intracel-lular stores, in particular, the endoplasmic reticulum1-6. Specific binding sites on the endoplasmic reticulum may participate in the InsP3-induced release of Ca2- from the Ca2- pool6-8. To examine the specific binding sites on the endoplasmic reticulum, we synthesized an arylazide derivative of InsP3 for photoaffinity labelling; InsP3 coupled to p-azidobenzoic acid (InsP3-pAB) using N,N′-carbonyldiimidazole (GDI) was obtained at a 9-11% yield. Here, we report that InsP3-pAB, but not an arylazide derivative of inositol-1,4-bisphophate (Ins(1,4)P2), causes the irreversible inhibition of InsP3-induced release of Ca 2- in saponin-permeabilized photo-irradiated macrophages. The irreversible inhibition by InsP3-pAB after photo-irradiation was prevented by a 10-fold excess of unmodified InsP3.
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