Direct Identification of Disulfide Bond Linkages in Human Insulin-Like Growth Factor I (IGF-I) by Chemical Synthesis

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Abstract
The primary structure of human IGF-I, except for the disulfide bond system, has been reported by Rinderknecht and Humbel. IGF-I afforded the corresponding characteristic peptide fragment on V8 protease digestion, which contained Cys6, Cys47, Cys48, and Cys52. Two possible fragments, Type I with Cys′-Cys47 and Cys48-Cys5t and Type II with Cyss-Cys48 and Cys47-Cys′, were synthesized. The disulfide bond systm of IGF-I was unequivocally determined to be the Type II form along with Cy818-Cys61. Interestingly, the Type I system was included in the disulfide bond isomer produced as the main by-product in the refolding step on IGF-I synthesis by the recombinant DNA method.