Secondary structural changes in the intact and the disulfide bridges cleaved beta-lactoglobulin A and B in solutions of urea, guanidine hydrochloride, and sodium dodecyl sulfate |
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Authors: | Kunio Takeda and Yoshiko Moriyama |
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Institution: | (1) Department of Applied Chemistry, Okayama University of Science, 700 Okayama, Japan |
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Abstract: | The relative proportions of -helix, -sheet, and unordered form in -lactoglobulin A and B were examined in solutions of urea, guanidine, and sodium dodecyl sulfate (SDS). In the curve-fitting method of circular dichroism (CD) spectra, the reference spectra of the corresponding structures determined by Chen et al. (1974) were modified essentially according to the secondary structure of -lactoglobulin B predicted by Creamer et al. (1983), i.e., that the protein has 17% -helix and 41% -sheet. The two variants showed no appreciable difference in structural changes. The reduction of disulfide bridges in the proteins increased -sheet up to 48% but did not affect the -helical proportion. The -helical proportions of nonreduced -lactoglobulin A and B were not affected below 2 M guanidine or below 3 M urea, but those of the reduced proteins began to decrease in much lower concentrations of these denaturants. By contrast, the -helical proportions of the nonreduced and reduced proteins increased to 40–44% in SDS. The -sheet proportions of both nonreduced and reduced proteins, which remained unaffected even in 6 M guanidine and 9 M urea, decreased to 24–25% in SDS. |
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Keywords: | -lactoglobulin A" target="_blank">gif" alt="beta" align="MIDDLE" BORDER="0">-lactoglobulin A -lactoglobulin B" target="_blank">gif" alt="beta" align="MIDDLE" BORDER="0">-lactoglobulin B secondary structure CD SDS |
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