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

Abstract

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.