Kinetic study on conformational change in a single molecular species, beta3, of beta-conglycinin in an acidic ethanol solution

The conformational change in a single molecular species, beta3, of beta-conglycinin in an acidic ethanol solution was kinetically studied by the stopped-flow technique, utilizing the intrinsic fluorescence of proteins and the fluorescence of 1-anilinonaphthalene-8-sulfonic acid (ANS) bound to the proteins. The time-course of the intrinsic fluorescence changes clearly showed the rate of conformational change below and above 25% ethanol to be quite different from each other. ANS could bind well to the protein in an ethanol concentration range of 15-25%. However, the rate of conformational change of the protein corresponding to that for ANS binding could not be obtained at less than 25% ethanol, while the rate of conformational change agreed well with that for ANS binding at more than 25% ethanol. In addition, the process showing the greatest and slowest ANS binding was not apparent in the denaturation of beta-conglycinin under the conditions employed. These results lead to the conclusions that the beta-conglycinin structure could be maintained in the mild molten globule-like denaturation state, and that various tertiary structural changes could take place without any significant effect on the high sensitivity of intrinsic fluorescence after the secondary structural changes.