BINDING OF MEDIUM-CHAIN FATTY-ACID ANIONS TO SOYBEAN BETA-CONGLYCININ

The binding isotherms of aliphatic medium-chain carboxylate anions (oc tanoate and decanoate) to soy beta-conglycinin have been measured by e quilibrium dialysis at 30-degrees-C in a Tris-HCl buffer, pH 8.0, cont aining 10 mM 2-mercaptoethanol. It has an intrinsic binding constant o f 663 M-1 for decanoate at 30-degrees-C. The number of binding sites o n the native beta-conglycinin was estimated to be 3. Decanoate binding was independent on the ionic strength and temperature of the incubati on medium. Decanoate binding was decreased when reductant was removed from the medium. The native tertiary structure with reduced sulfhydryl group was required maximal binding of decanoate to beta-conglycinin. A decrease in decanoate binding occurred when pH of the medium was rai sed from 8.0 to 10.0, indicating that the presence of positively charg ed protein sites were required for the binding. The binding affinity w as enhanced by an increase in chain length of the ligand, suggesting t hat the major binding energy is derived from hydrophobic interactions between non-polar tail of fatty acid and hydrophobic regions of protei n.