Calcitonin (Ct) is a 32-residue peptide hormone that is mainly known for its hypocalcemic effect and the inhibition of bone resorption. Our previous studies have led to potent, side-chain lactam-bridged human Ct (hCt) analogues [Kapurniotu, A. Kayed, R., Taylor, . & Voelter W. (1999) Eur. J. , 606±618; Kapurniotu, A. & Taylor, . (1995)J. Med. , 836±847]. We have hypothesized that a possibly type Ibturn/bsheet confor-mation in the region 17±21 may play an important role in hCt bioactivity. .
