摘要：

We have used the light scattering method and the theory of polycondensation equilibria to determine the thermodynamics of association in solution of a number of divalent haptens with pure preparations of rabbit anti-arsanilic antibody. The antibody molecules are linked together by the haptens containing two arsanilic acid groups, but the weight average degree of association rarely exceeds two. The association is reversible and the extent of association is clearly governed by an intrinsic equilibrium constant characteristic of the haptenic group and the antibody site. The average free energy of formation of the hapten-antibody bond is -7.4 ± 0.2 kcal./mole at antibody concentration of about 1 g./l. for the most strongly interacting haptens. This average value is lowered to -8.3 kcal, when the antibody concentration is reduced 10-fold, and this is interpreted as an indication of some inhomogeneity in the antibody sites. At a given antibody concentration the free energy values for the haptens investigated cover a range of about 1 kcal, and the variation is consistent with the expected contribution of steric hindrance. Measurements of the temperature dependence of the extent of association give ΔH° = -0.8 ± 2.6 kcal./mole and ΔS° = 22 ± 9 cal./mole/deg. These results indicate the liberation of a number of water molecules from the hapten and antibody molecules when the bond forms.

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