des-Ser2 salmon calcitonin: a biologically potent synthetic analog.

We studied the biological activity of a synthetic analog of salmon calcitonin (SCT), from which the serine2 residue within the amino-terminal disulfide ring had been omitted (des-Ser2SCT). This analog proved to be indistinguishable from SCT with respect to hypocalcemic activity in vivo, displacement of [125I]SCT from rat renal membranes, and accumulation of cAMP in incubated renal cortical slices. des-Ser2SCT was twice as potent as SCT with respect to adenylate cyclase activation in renal membranes. Since the deletion did not impair biological activity, it appears that the function of the intact ring structure does not critically depend on its encompassed peptide chain length. (Endocrinology 108: 831, 1981)