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Polypeptides. LVI. Effect of lithium bromide and of temperature on the conformation of a copolymer of glutamic acid and lysine

✍ Scribed by Koichi Morita; Elizabeth R. Simons; Elkan R. Blout

Publisher
Wiley (John Wiley & Sons)
Year
1968
Tongue
English
Weight
481 KB
Volume
6
Category
Article
ISSN
0006-3525

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✦ Synopsis

By usiiig optical rotatory dispersion measurements, the helix content of poly G 1 ~5 ~L y s 5 ~ has been investigated and compared with that of poly G1u20Lys20AlaGa in aqueous solutions. RLeasurements were made at pH 3 and at pH 8 in various concentrations of lithium bromide. Various factors affecting helix stabilization are considered and their perturbation by lithium bromide is related to the shape of the observed transition curves. A residual helis content of 12% in 8M LiBr, based upon a ba of +lo0 for a fully random conformation, was observed for poly G1n50Lys50 a t pH 3 and 8. The loss of helix content of poly G l ~~~L y s ~~ as a function of temperature is also reported. AH is approximately -6.9 kcal./mole for the overall trarisition, compared to -6.5 kcal./mole for poly Glu*0Lys20Ala60. The midpoint of the broad transition is near 40°C. at pH 3, but much lower, a t -10 to O"C., at pH 8. These results are discussed in terms of the stabilizing factors for the partial helix content of the polypeptides.

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