Somatomedin-C Shares the Carboxy-Terminal Antigenic Determinants With Insulin-Like Growth Factop-I

Insulin-like growth factor I is a human plasma peptide with strong homology to human proinsulin. Many lines of evidence suggest that somatomedin-C and insulin-like growth factor I are identical molecules. However, no structural data regarding the carboxy-terminal end of somatomedin-C has yet been produced. We report a region-specific immunoassay directed against the carboxy-terminal end of insulin-like growth factor I. Somatomedin-C and insulin-like growth factor I are indistinguishable in this region-specific immunoassay. Insulin-like activity II and multiplication stimulating activity show partial cross reaction in this immunoassay. This study provides the first evidence about the carboxy-terminal portion of somatomedin-C and re-emphasizes that somatomedin-C and insulin-like growth factor I should be considered identical molecules.