ISSN:
0006-3525
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Copolymers of L-lysine and L-isoleucine [poly(L-Lysf,L-Val1 - f)] containing 4-15% isoleucine were investigated using potentiometric titration and circular dichroism (CD) spectroscopy. With increasing isoleucine content, β-sheet formation is favored over α-helix formation at high pH and room temperature. The fraction of β-sheet present, as a function of pH, calculated from titrations of poly(L-Lys85.2,L-Ile14.8), agreed well with data obtained from CD studies for the same copolymer. Thermodynamic parameters were determined from titrations using the method of Zimm and Rice; the partial free energy (ΔG°C → β) at 25° for the coil-to-β-sheet transition for isoleucine was estimated to be -515 cal/mol; from the temperature dependence of free energy, the partial entropy (ΔS°cβ), and the partial free enthalpy (ΔH°c → β) of the coil → β transition for isoleucine is estimated to be 2.6 e.u. and 260 cal/mol, respectively. The partial thermodynamic parameters obtained for lysine are in good agreement with literature values. It is concluded from these studies that isoleucine has a very high potential for a β-sheet formation.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/bip.1977.360160103
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