Direct identification of a novel disulfide bond linkage system of new isolated isomer (isomer V) in recombinantly produced h-IGF-I

Insulin-like growth factor I(IGF-I or somatomedin C) is a serum polypeptide with three intramolecular disulfide bonds. In the course of synthesis by t he recombinant DNA method, three disulfide bond Isomers, all of which have Cys(18)-Cys(61) with three combinations of two disulfide bonds formed by Cy s(6), Cys(47), Cys(48) and Cys(52), were identified. Natural type, isomer I I, was proved to have a Cys(6)-Cys(48), Cys(18)-Cys(61), Cys(47)-Cys(52) di sulfide bond system. Non; the fourth isomer, isomer V which doesn't have Cy s(18)-Cys(61) disulfide, has been isolated, and its novel disulfide bond li nkage system was identified by a chemical synthetic method, The supposed co nformation constrained in 3D structure for isomer V would be discussed for its biological activity.