Sequence analysis of somatomedin-C: confirmation of identity with insulin-like growth factor I.

Somatomedin-C (Sm-C) was purified from Cohn fraction IV of human plasma by previously published methods. Purity was established by SDS polyacrylamide electrophoresis followed by silver staining of the gel. Amino acid analysis of an acid hydrolysate revealed no significant discrepancies from the amino acid composition of insulin-like growth factor I (IGF-I). The first 24 residues beginning at the amino terminal glycine were identical to the corresponding residues in IGF-I. Tryptic and chymotryptic degradation followed by determination of the amino acid composition and sequence of the resultant peptides was used to complete the primary structure of Sm-C. The results of these studies document that Sm-C and IGF-I are identical peptides, thus supporting previous observations that Sm-C and IGF-I are qualitatively and quantitatively indistinguishable in radioligand and biological assay systems.