ISSN:
0006-3525
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The optical rotatory dispersion of L-lysine oligopeptides (Lysn, n = 2-22) in solution was measured in water and in 50% methanol. A gradual change with increasing chain length in the ORD curves of the oligomers was observed at pH 4. 3. Not even a chain of 22 residues had ORD identical with that of high molecular weight poly-L-lysine. A plot of the average molar residue rotation at 233 nm versus 1/n (where n is the chain length) resulted in a straight line with an intercept of -1900, representing the internal residue rotation of a lysine residue in the random conformation, and a slope of +6200 representing the large end effect. At pH 11.9 a stright line is obtained up to n = 12 after which it deviates from the initial slope indicating onset of helicity. Extrapolation of the initially straight line to tire higher n's provided the necessary zero-helicity values for calculation of helicity. The highest oligolysine (n = 22) showed at pH 11. 9 13% helicity, which on adding methanol to 50% increased to about 50% helicity. It is shown that helix-coil data which are usually obtained from the temperature dependence of helicity can be obtained from the dependence of helicity on chain length applying the statistical theory. For the methanol-water system the cooperativity parameter v was calculated to be in the range 0.024-0.060, with corresponding equilibrium constants w of 1.32-1.43. The helical structure was calculated to be less stable in water than in methanol-water by about 250 calories per residue.
Additional Material:
9 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/bip.360100703
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