02957naa a2200349 a 450000100080000000500110000800800410001902400360006010000160009624501120011226000090022452019320023365000140216565000380217965000440221765000120226165000130227365000190228665000170230565000250232265000220234765000200236965000120238965000120240165300230241365300230243665300200245965300310247970000180251070000130252877300660254121651282024-06-26       1996    bl uuuu     u00u1 u    #d7 a10.1017/s0022029900031575.2DOI1 aBOYE, J. J.  aEffects of physicochemical factors on the secondary structure of beta-lactoglobulin.h[electronic resource]  c1996  aAbstract: Fourier transform infrared spectroscopy and differential scanning calorimetry were used as complementary techniques to study changes in the secondary structure of beta-lactoglobulin under various physicochemical conditions. The effects of pH (3-9), NaCl (0-2 M), and lactose, glucose and sucrose (100-500 g/l) in the temperature range 25-100 degrees C on the conformation sensitive amide I band in the i.r. spectrum of beta-lactoglobulin in D2O solution were examined. The 1692 cm-1 band in the amide I band profile had not been definitively assigned in previous studies of the i.r. spectrum of beta-lactoglobulin. The decrease in this band at ambient temperature with time or upon mild heating was attributed to slow H-D exchange, indicating that it was due to a structure buried deep within the protein. The disappearance of the 1692 cm-1 band on heating was accompanied by the appearance of two bands at 1684 and 1629 cm-1, assigned to beta-sheets. The 1692 cm-1 band was therefore attributed to a beta-type structure. beta-Lactoglobulin showed maximum thermal stability at pH 3 and was easily denatured at pH 9. On denaturation, the protein unfolded into more extensive random coil structures at pH 9 than at pH 3. After 10 h at pH 9 (25 degrees C), beta-lactoglobulin was partly denatured. Heating to 60-80 degrees C generally resulted in the loss of secondary structure. At all pH values studied, two new bands at 1618 and 1684 cm-1, characteristic of intermolecular beta-sheet structure and associated with aggregation, were observed after the initial denaturation. Differential scanning calorimetry studies indicated that the thermal stability of beta-lactoglobulin was enhanced in the presence of sugars. The Fourier transform i.r. results obtained provide evidence that sugars promoted the unfolding of beta-lactoglobulin via multiple transition pathways leading to a transition state resisting aggregation.  aDeuterium  aDifferential scanning calorimetry  aFourier transform infrared spectroscopy  aGlucose  aHydrogen  aLactoglobulins  aPharmacology  aProtein denaturation  aProtein structure  aSodium chloride  aSucrose  aLactose  aChemical phenomena  aChemistry physical  aHot Temperature  aHydrogen Ion Concentration1 aISMAIL, A. A.1 aALLI, I.  tJournal of Dairy Researchgv. 63, n. 1, p. 97-109, Feb. 1996.