A combination of equilibrium dialysis and ultrafiltration has been used to demonstrate the conservation of charge in the interaction between bovine serum albumin and methyl orange in Tris-HCl buffer, pH 7.4, I = 0.05 M; and also in the dimerization of α-chymotrypsin in acetate/chloride buffer, pH 3.9, I = 0.11 M, containing various concentrations of indole (0-10 mM) in order to displace the equilibrium position towards monomer. In the former study the magnitude of the negative charge on the albumin was shown to increase linearly with the number of molecules of methyl orange bound to the protein, the observed slope (0.96 ± 0.08) of this relationship being in excellent agreement with that predicted on the basis of charge conservation for attachment of the univalent, negatively charged methyl orange ligand. In the study of α-chymotrypsin, the net charge (expressed per monomeric enzyme unit) was + 10 in solutions in which the mole fraction of monomer varied between 0.47 and 0.88, the extent of this range having been established by means of constituent association equilibrium constant obtained from sedimentation equilibrium studies. © 1983.
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