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Title: Microcalorimetry of cyclodextrin interactions with amino acids and proteins
Author: Lovatt, Michelle
ISNI:       0000 0001 3613 026X
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1997
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The interaction of a range of cyclodextrins with amino acids, both free and in proteins has been investigated using sensitive microcalorimetry and spectroscopic techniques. With a view towards possible applications in chiral separation technologies, isothermal titration calorimetry (ITC) was used to study the complexation of cyclodextrins with the enantiomers of α-amino acids by competition with p-nitrophenolate or p-aminobenzoic acid under various pH conditions. It was found the majority of amino acids showed no complexation. However, complexes of alpha-cyclodextrin with phenylalanine, and tryptophan demonstrated small, but distinct, differences in dissociation constants for their separate enantiomers. Thermodynamic parameters (Kd, ΔH°, ΔG° and ΔS°) were obtained for all amino acids which showed complexation. Isothermal titration (dilution) microcalorimetry was also used to study the effect of cyclodextrins on the dissociation of bovine insulin in aqueous solution under various conditions. Thermodynamic data indicate that cyclodextrins increased dissociation of insulin oligomers in a manner consistent with their interaction with protein side chains. For example, the addition of methyl-P-cyclodextrin makes dissociation significantly more endothermic and reduced the apparent dimer dissociation constant by more than two orders of magnitude. Differential scanning calorimetry (DSC) was used to examine the effects of cyclodextrins on thermal unfolding of proteins. It was found that the mean unfolding temperature (Tm) of cytochrome c and lysozyme was reduced in the presence of cyclodextrins. Such observations indicate that the weak interaction of cyclodextrins with exposed amino acid residues promotes unfolding and dissociation of proteins. The possibility that such interactions may facilitate the use of cyclodextrins as 'chaperone-mimics' in the refolding of denatured protein has been explored with the enzyme phosphoglycerate kinase (PGK). It was found that the presence of cyclodextrins or N-methylacetamide during thermal denaturation significantly enhanced the regain of enzyme activity of PGK by up to forty percent.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Protein folding; Calorimetry