Purification and assay of intact human basic fibroblast growth factor using heparin-sepharose chromatography

Abstract

Intact human hepatoma derived basic fibroblast growth factor (bFGF) is a cationic 18 400-molecular-weight polypeptide, which stimulates the proliferation of 3T3 and endothelial cells at 1 ng/ml. bFGF has a strong affinity for heparin, and can be purified to homogeneity from human hepatoma cells using heparin-Sepharose chromatography. A three-step procedure is used: (a) extraction of the cells with 1M NaCl at pH 7.5; (b) Bio-Rex 70 cation exchange chromatography; and (c) heparin-Sepharose chromatography. The molecular weight of bFGF depends on the pH of the cell extraction step. When extracted at neutral pH, intact bFGF is obtained with a molecular weight of 18 400, however when extracted at pH 3.5 to 4.5 the molecular weight of bFGF is about 16 500. Lowering the molecular weight by acid pH extraction can be inhibited with a mixture of the proteinase inhibitors, PMSF, leupeptin, and pepstatin. These results suggest that degradation of bFGF is the result of cleavages by acid proteinases. It has been determined by amino acid sequence data and western blot analysis that the cleavages occur at the amino terminus of bFGF. The lower molecular weight form of bFGF has the same biological activity and exhibits the same chromatographic behavior on heparin-Sepharose as does intact bFGF.