By use of a published method for the isolation of the 11S protein of sunflower seed in a homogeneous form, a procedure has been outlined for obtaining polyphenol-free 11S protein. Neither the gel filtration nor the PAGE pattern of the protein was affected by the method of polyphenol removal. The nearand far-ultraviolet circular dichroism spectrum of the protein was nearly the same as that of the protein containing polyphenols. Binding of chlorogenic acid by the polyphenol-free 11S protein of sunflower seed has been measured as a function of pH, salt concentration, and temperature. Increase in pH or salt concentration decreased the binding. Binding at 45 °C was less than at 30 °C; it was completely abolished at 55 °C. Addition of Na2S03 (0.01 M), dioxane (4%), or urea (8 M) to the buffer abolished the binding. Analysis of the binding data by Scatchard equation and Hill equation showed that binding affinity was not affected by pH or salt, but the maximum number of binding sites was reduced. Decreasing the pH dissociated the 11S protein to lower molecular weight proteins. This effect was reversed by the addition of NaCl or Na2S03.

This study uses mutants of human carbonic anhydrase (HCAII) to examine how changes in the organization of water within a binding pocket can alter the thermodynamics of protein–ligand association. Results from calorimetric, crystallographic, and theoretical analyses suggest that most mutations strengthen networks of water‐mediated hydrogen bonds and reduce binding affinity by increasing the enthalpic cost and, to a lesser extent, the entropic benefit of rearranging those networks during binding. The organization of water within a binding pocket can thus determine whether the hydrophobic interactions in which it engages are enthalpy‐driven or entropy‐driven. Our findings highlight a possible asymmetry in protein–ligand association by suggesting that, within the confines of the binding pocket of HCAII, binding events associated with enthalpically favorable rearrangements of water are stronger than those associated with entropically favorable ones.

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