The somatomedin-binding protein isolated from a human hepatoma cell line is identical to the human amniotic fluid somatomedin-binding protein.

Serum-free medium conditioned by the human hepatoma cell line HEP G2 was shown to contain a somatomedin-binding protein with a relative molecular mass of about 35,000. This binding protein was purified to homogeneity by the use of immunoaffinity chromatography and subsequent size exclusion chromatography. Antibodies for the immunoaffinity step were raised in rabbits against a previously isolated human amniotic fluid somatomedin-binding protein. The total composition and N-terminal amino acid sequence showed the protein to be identical to the binding protein from human amniotic fluid. Both have the N-terminal structure Ala-Pro-Trp-Gln-. The HEP G2 cell line offers a useful model to study the regulation of the synthesis and secretion of human somatomedin-binding proteins.