Effect of low pH and heparin on the structure of acidic fibroblast growth factor.

Changes in the fluorescence of the single tryptophan of acidic fibroblast growth factor have been used to monitor the effect of low pH on the conformation of the molecule, and the consequences of heparin binding and high ionic strength under such conditions. These studies demonstrate that the conformation of the protein changes reversibly below pH 5, and that heparin, depending on the conditions, may either prevent that change or induce a new irreversible modification of the structure, which runs parallel to the partial inactivation of the protein. It is also demonstrated that secondary heparin-binding sites appear at low pH, which favor the formation of precipitates at some protein/heparin ratios. Precipitation and inactivation of fibroblast growth factor at low pH may hinder its wound-healing activity, since acidification seems frequent in wounds.