M/sub r/ 25,000 heparin-binding protein from guinea pig brain is a high molecular weight form of basic fibroblast growth factor

A M/sub r/ 25,000 form of basic fibroblast growth factor (bFGF) has been isolated from guinea pig grain along with the typical M/sub r/ 18,000 form. Both forms were purified to homogeneity by a combination of heparin-affinity chromatography and ion-exchange chromatography on an FPLC Mono S column. The M/sub r/ 25,000 form, like the M/sub r/ 18,000 form was not eluted from the heparin-affinity column with 0.95 M NaCl, but was eluted with 2 M NaCl. The M/sub r/ 25,000 guinea pig protein stimulated plasminogen activator production by cultured bovine capillary endothelial cells in a dose-dependent manner at concentration of 0.1-10 ngml, the same range that was effective for guinea pig and human M/sub r/ 18,000 bFGFs. The binding of human 125I-labeled bFGF to baby hamster kidney cells is inhibited equally by the M/sub r/ 25,000 guinea pig protein and the M/sub r/ 18,000 guinea pig and human bFGFs. Polyclonal antibodies raised against human bFGF recognize both the M/sub r/ 25,000 and 18,000 guinea pig proteins in an immunoblot analysis. In a radioimmunoassay, both the M/sub r/ 25,000 and M/sub r/ 18,000 guinea pig proteins compete equally well with iodinated human bFGF for binding to the anti-human bFGF antibodies. When treated with low concentrations of trypsin, the M/sub r/ 25,000 guinea pig bFGF was converted to a M/sub r/ 18,000 protein. These results show that the two molecules are closely related and suggest that the M/sub r/ 25,000 protein shares substantial homology with the M/sub r/ 18,000 bFGF