Analysis of the interaction between human plasma fibronectin and gelatin by affinity electrophoresis

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Abstract
The interaction between human plasma fibronectin and gelatin was analyzed by affinity electrophoresis, in which the fibronectin was subjected to electrophoresis in a 4% polyacrylamide gel in the presence and absence of gelatin, as an affinity ligand, and the fibronectin band was stained by an immunoblotting method. The apparent dissociation constants (Kd) of fibronectin for gelatin were calculated from affinity plots based on the original affinity equation at different pHs, urea concentrations, and temperatures. The fibronectin exhibited much lower affinity in the presence of urea. The Kds at 37°C were 1.49 × 10−7 M, 2.50 × 10−6 M, and 3.58 × 10−6 M with 2 M, 3 M, and 4 M urea, respectively. The van't Hoff plots of Kd values against absolute temperature (T) showed that the value of log Kd decreased in proportion to the increase in the value of 1/T within the range of 15–50°C. The standard enthalpy, the standard free energy change at 37°C, and the entropy change at 37°C for association were calculated to be −124.7 kJ/mol, −33.23 kJ/mol, and −295.1 J/mol/deg, respectively. These results suggest that a hydrophilic interaction, such as hydrogen bond or van der Waals interaction, plays an important role in the binding of plasma fibronectin to gelatin.