Binding of globular proteins to DNA from surface tension measurement.

Extent of binding (gammap) of globular proteins to calf-thymus DNA have been measured in mole per mole of nucleotide as function of equilibrium protein concentration. We have exploited measurement of the surface tension of the protein solution in the presence and absence of DNA to calculate the binding ration (gammap). Interaction of bovine serum albumin with DNA has been studied at different pH. Interaction of bovine serum albumin with DNA has been studied at different pH, ionic strength and in presence of Ca2+. Interaction of BSA with denatured DNA has also been investigated. Binding isotherms for other globular proteins like beta-lactoglobulin, alpha-lactalbumin and lysozyme have been compared under identical physicochemical condition. It has been noted with considerable interest that globular form of protein is important to some extent in protein-DNA interaction. An attempt has been made to explain the significance of difference in binding ratios of these two biopolymers in aqueous medium for different systems in the light of electrostatic and hydrophobic effects. Values of maximum binding ration (gammap(m)) at saturated level for different systems have been also presented. The Gibb's free energy decrease (-deltaG0) of the binding of proteins to DNA has been compared more precisely for the saturation of binding sites in the DNA with the change of activity of protein in solution from zero to unity in the rational mole fraction scale.

Stimulation of the absorption of macromolecules in Giardia lamblia infected mice intestine.

The absorption of 125I-labelled bovine serum albumin, gamma-globulin and alpha-lactalbumin was considerably enhanced in G. lamblia infected Swiss mice intestine compared to uninfected controls. The binding of 125I-proteins to brush border membrane was however, significantly (P less than 0.01) low in infected animals. Kinetic studies with gamma-globulin binding to brush borders revealed a decrease in the number of binding sites in infected animals (1.52) compared to controls (2.86 micrograms/mg protein) with no change in the affinity constant (47.60 micrograms/ml) under these conditions. These findings suggest that G. lamblia infection in mice leads to enhanced macromolecular absorption which seems unrelated to the binding of proteins to epithelial cell surface.