Isolation of an Amino Terminal Extended Form of Basic Fibroblast Growth Factor

Extraction of bovine pituitaries in the presence of enzyme inhibitors (2 mM PMSF, 2 mM sodium tetrathionate, 15 microM pepstatin A, and 1 mM EDTA) resulted in the isolation of two distinct forms of basic fibroblast growth factor. Partial characterization of both molecules showed one form to be identical to basic FGF(1-146) which has already been reported by our laboratory. The second form was estimated by SDS-PAGE to have a molecular weight of 17,000 Daltons which is slightly larger than that of basic FGF(1-146). Amino acid analysis shows the presence of 8 new residues more than basic FGF(1-146) which accounts for the difference in molecular weight. Gas-phase sequencing of this molecule indicated that it bears a blocked amino terminus. Furthermore, this higher molecular weight form of basic FGF did not show immunoreactivity with antibodies specific for the amino terminus of basic FGF(1-146) but cross reacted with antibodies generated against midportion fragments of basic FGF(1-146), indicating that the molecule is amino terminally extended. Like basic FGF(1-146), the molecule is a potent mitogenic factor for vascular endothelial cells. Taken together these results demonstrate the existence of a precursor form of basic FGF which is extended by 8 residues at the amino terminus with the first residue being blocked.