Study on the heat-induced conformational changes of β-conglycinin by FTIR and CD analysis

Abstract

The influence of temperature on conformational changes was investigated for β-conglycinin, which is one of the main storage proteins of soybean seeds, using Fourier transform infrared (FTIR) and circular dichroism (CD) methods. FTIR spectra have been measured at the temperature range 25–80° C for 10% β-conglycinin in 35 mmolldm 3 phosphate buffer at pD 7.6. The band at 1639 cm −1 indicated the degree of denaturation and the band at 1618 cm −1 was considered to reflect the formation of intermolecular β-sheet structures. The decrease in the band at 1639 cm −1 indicated that heat-denaturation of β-conglycinin occurred at ~65°C and proceeded with increasing temperature in the range 65–80°C. On the other hand, with increasing temperature, the band at 1618 cm −1 began to increase at ~65°C, and seemed to saturate when the temperature was >75°C. The results of CD spectroscopies are in good agreement with results from FTIR. These results show that the conformational states of heat-denatured β-conglycinin are different depending on temperature. However, once heat-denaturated β-conglycinin was cooled, partial refolding of the unfolded structure was induced, and it was difficult to elucidate conformational differences between β-conglycinin which was treated with different temperatures by CD analysis.