par Barel, André ;Prieels, Jean-Paul
Référence European journal of biochemistry / FEBS, 50, 2, page (463-473)
Publication Publié, 1975
Article révisé par les pairs
Résumé : Various insoluble α‐lactalbumins (bovine, bovine glyco‐α‐lactalbumin, human and human nitrated) have been prepared by coupling these proteins on to an agarose gel with use of cyanogen bromide. Some intrinsic fluorescence properties, such as fluorescence maximum and pH dependence, were considered in order to study conformational changes of the α‐lactalbumins covalently bound to an insoluble matrix. Examination of the pH–fluorescence profiles as well as the position of the maximum in the emission spectrum indicates that the Sepharose matrix does not appreciably modify the conformation of human and bovine glyco‐α‐lactalbumins. Some change in the fluorescence spectrum (peak shifting towards longer wavelength) was observed for bovine α‐lactalbumin and appeared to be due to alteration of the environment of the tryptophan side‐chains in the protein upon coupling to the agarose gel. The emission spectrum of the insolubilized human nitrated α‐lactalbumin indicates that the polypeptide chain of this protein gained some native conformation when covalently bound to the carrier. The extrinsic fluorescence of a bound dye, such as 2‐p‐toluidinylnaphthalene‐6‐sulfonate, was used to study and to compare the hydrophobic sites on the surface of insoluble α‐lactalbumins with the same proteins in solution. Considering the fluorescence properties of the protein · dye complexes it was found that both states of α‐lactalbumins (insoluble and free in solution) bind the dye with similar association constants. However, the positions of the maxima in the emission spectra are all somewhat shifted towards longer wavelengths, suggesting that the dye binding site is located in a more polar environment when the proteins are bound to agarose. The human nitrated α‐lactalbumin retains about equal possibility of binding this fluorescent dye. As shown for bovine α‐lactalbumin in solution, the binding of 2‐p‐toluidinylnaphthalene‐6‐sulfonate towards the various insoluble α‐lactalbumins was not appreciably modified by the presence of various small compounds such as sugars and UDP, which are effectors in the lactose synthetase function. Copyright © 1975, Wiley Blackwell. All rights reserved