TEMPERATURE-INDUCED FOLDING CHANGES OF BETA-LACTOGLOBULIN IN HYDRO-METHANOLIC SOLUTIONS

It has been demonstrated using circular dichroism that methanol induce s important structural changes of beta-lactoglobulin (BLG). The second ary structure of BLG dissolved in 45% methanol (v/v) at 30-degrees-C ( dielectric constant epsilon almost-equal-to 50) is predominantly alpha -helical and unable to complex retinol any more. However, when the die lectric constant of such a medium is raised back to epsilon almost-equ al-to 70 by decreasing the temperature, both the refolding of BLG into a beta-structure and the formation of the retinol/BLG complex are obs erved On the other hand, in the case of BLG solution in 30% methanol, the decrease of the dielectric constant from epsilon almost-equal-to 6 9 to epsilon almost-equal-to 53 by heating from 20-degrees-C to 60-deg rees-C leads to the transition from a predominantly beta-structure int o a predominantly random one and the dissociation of the retinol/BLG c omplex. The reversibility of the conformation changes by cooling was d emonstrated by circular dichroism curves and tryptophan fluorescence. The retinol fluorescence intensity could not be completely recovered.