C 10 ‐O e ‐N‐(4‐azido‐5‐ 125 iodo salicyloyl)‐β‐alanyl‐β alanyl ryanodine (Az‐βAR), a novel photo‐affinity ligand for the ryanodine binding site

A high affinity, photoactivatable, radio‐iodinated ligand for the ryanodine binding site(s) of the sarcoplasmic reticulum calcium‐release‐channel, C 10 ‐O eq ‐N‐(4‐azido‐5‐ 125 iodo salicyloyl)‐β‐alanyl‐β‐alanyl ryanodine (Az‐βAR), was synthesized at a specific activity of 1400mCi/mmol. Prepared by condensing the versatile synthon, N‐(4‐azido‐5 125 iodo salicyloyl)‐β‐alanine with C 10 ‐O eq ‐β‐alanyl ryanodine, Az‐βAR, like [ 3 H] ryanodine, does not demonstrate saturation binding kinetics. 127 Az‐βAR exhibits an IC 50 of 27.2 ± 2 × 10 −9 M (mean ± SD) compared to ryanodine's 6.2 ± 0.4 × 10 −9 M for the ryanodine receptor/calcium release channel of sarcoplasmic reticulum vesicles isolated from rabbit skeletal muscle.