Effect of temperature on tryptophan fluorescence of beta-lactoglobulin B.
The effect of heat on the conformation of bovine beta-lactoglobulin has been studied using intrinsic fluorescence spectroscopy. Changes in the intensity, wave-length of maximum emission and emission peak width at half height of tryptophan fluorescence over the range 15-90 degrees C at pH 6.4-6.5 has allowed the environments of the two tryptophans in the molecule to be discriminated. At 20 degrees C both tryptophans are in hydrophobic environments. As the temperature is raised the conformation changes such that at about 50 degrees C one of the tryptophans is transferred to a more polar environment accessible to solvent. Conformational changes appear to be reversible if the protein is cooled to 20 degrees C after heat treatments up to 70 degrees C. Above 70 degrees C the second tryptophan residue becomes exposed to solvent. Complete exposure of one residue occurs at 80 degrees C while the other is still partially buried even at 90 degrees C. When the protein is then cooled to 20 degrees C the conformational changes appear to be irreversible with only one tryptophan residue returning to the hydrophobic interior of the molecule.
D000818:Animals; D002417:Cattle; D006863:Hydrogen-Ion Concentration; D007782:Lactoglobulins; D008433:Mathematics; D011487:Protein Conformation; D011489:Protein Denaturation; D013050:Spectrometry, Fluorescence; D013696:Temperature; D014364:Tryptophan / Q000032:analysis
D007782:Lactoglobulins; D014364:Tryptophan