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  • 1
    ISSN: 1573-4943
    Keywords: ovalbumin ; CD studies ; guanidine ; urea ; sodium dodecyl sulfate ; conformation ; secondary structure ; denaturation-renaturation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract By simulation of the circular dichroic spectra (Greenfield and Fasman (1969)) and using reference spectra of Chen et al. (1974), native ovalbumin was estimated to contain 33% α-helix, 5% β-structure, and 62% random coil. Ovalbumin resisted conformational changes in solutions of urea and of SDS. However, guanidine induced transition, starting at about 2 M and completing at about 4.5 M. At concentrations exceeding 4.5 M guanidine, ovalbumin existed as 6–7% α-helical, 12–13% β-structure, and 80–81% random coil. Ovalbumin after denaturation in 6 M guanidine or in 8 M urea (incubated at 4°C for 24 hr) did not recover the native conformation but acquired a new conformation in each case, with a somewhat destabilized helical structure.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-4943
    Keywords: sulfhydryl-blocked ovalbumin ; secondary structure ; conformation ; circular dichroic studies ; reduced ovalbumin ; denaturation profiles in guanidine, urea, and sodium dodecyl sulfate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Sulfhydryl groups of ovalbumin were chemically modified under denaturing conditions in the absence and presence of dithiothreitol, and effects on the secondary structure of the protein were investigated by circular dichroic (CD) measurements. The contents of α-helix, β-structure, and “random coil” (unordered, nonrepetitive structure) were estimated by simulation of the CD spectra and using the parameters established by Chen et al. The principal findings were these: (1) Modification of the four free sulfhydryl groups [with 5,5′-dithiobis(2-nitrobenzoic acid), iodoacetate, or iodoacetamide] caused ovalbumin molecule to unfold partially and to undergo primarily helix-to-β structure transition. (2) Cleavage of the disulfide bond did not lead to a further conformational change in the sulfhydryl-modified ovalbumin. (3) The remaining helical structure existed in a destabilized state with increased chain flexibility, as the modified protein was very susceptible to denaturation by guanidine and urea. (4) Further evidence for increased chain flexibility was provided by the finding that sodium dodecyl sulfate (SDS) induced helix formation in the sulfhydryl-modified, but not native, ovalbumin. And (5), since both nonreduced and reduced proteins, with their sulfhydryl groups blocked, displayed similar transitions in solutions of guanidine, urea, and SDS suggested that the single disulfide bond did not physically constrain the ovalbumin molecule.
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  • 3
    ISSN: 1573-4943
    Keywords: Succinylated ovalbumins ; acetylated ovalbumins ; secondary structure ; conformation ; circular dichroism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In order to determine the effect of chemical modification of the ε-amino groups on the secondary structure of ovalbumin, we prepared six acetylated (17, 36, 54, 70, 82, and 98%) and four succinylated derivatives (25, 50, 72, and 97%) of the protein. Native ovalbumin and the acylated derivatives were homogeneous as revealed by the electrophoretic pattern. The UV-absorption and fluorescence spectra changed progressively with the extent of modification. However, circular dichroic (CD) studies indicated that acylation of 15 of the 20 lysine residues had little effect on the secondary structure of ovalbumin. Acylation of the remaining five lysine residues resulted in a fairly severe change in the secondary structure. The α-helical content decreased from about 31% in the native state to 16.5% in the 97% succinylated ovalbumin and to 21.5% in the 98% acetylated derivative. A comparison of these data with the spectral and hydrodynamic data of Qasim and Salahuddin (1978) suggested that the secondary structure of ovalbumin is more resistant to acylation than is the tertiary structure and, thus, the tertiary and the secondary structures are, to some extent, mutually independent. Raising thepH to 11.2 did not alter the secondary structure of ovalbumin and increasing the ionic strength by more than 20-fold did not reverse the loss of helical structure in 97% succinylated protein. These two observations suggest that the change in secondary structure upon maximal acylation may not only involve electrostatic effects, but also certain other factors, such as steric hindrance due to the entering bulky groups.
    Type of Medium: Electronic Resource
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