Binding of chlorogenic acid by the isolated polyphenol-free 11S protein of sunflower (Helianthus annuus) seed.

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 near-and farultraviolet
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.