Complexation of basic fibroblast growth factor with gelatin

Polyion complexation between basic fibroblast growth factor (bFGF) and gelatin was studied by the turbidity change of mixed solution, heparin high performance liquid affinity chromatography (HPLAC), and isoeletric eletrophoresis. When an aqueous solution of acidic gelatin with an isoelectric point (IEP) of 5.0 was mixed with that of bFGF, the turbidity of the mixed solution increased with time; whereas basic gelatin with an IEP of 9.0 did not cause any solution turbidity. A maximum turbidy of the mixed bFGF and acidic gelatin solution was observed around a bFGF/gelatin molar ratio of 1.0, irrespective of the gelatin concentration and solution temperature. The solution turbidity decreased with an increase in the ionic strength of the mixed solution. Complexation of bFGF with acidic gelatin was slower than that with poly(acrylic acid) probably because of the lower density of gelatin negative charge than that of poly(acrylic acid). HPLAC study revealed that complexation of bFGF with the acidic gelatin reduced the affinity of bFGF for heparin, in contrast to the basic gelatin, although the extent became smaller with the increasing ionic strength of the solution. An electrophoretic experiment showed that the IEP of bFGF shifted to a lower value after its gelatin complexation. These findings indicate that an electrostatic interaction is the main driving force for the complexation between acidic gelatin and basic bFGF.