Amino acid sequence of a variant pro-form of insulin-like growth factor II.

Human serum contains, in addition to the "classical" 7.5-kDa insulin-like growth factors (IGFs) I and II, small amounts of larger IGF-II. A 10-kDa IGF-II was isolated by gel filtration, immunoaffinity chromatography, and reversed-phase HPLC. Upon amino acid sequence determination, a substitution of Cys-Gly-Asp for Ser-33 was found as well as a COOH-terminal extension of 21 residues (E peptide). These sequence differences suggest that 10-kDa IGF-II is a precursor of a variant IGF-II. Since the substitution is not located at a known intron/exon hinge region, the finding of this variant IGF-II is evidence for the presence of more than one gene for IGF-II.