Abstract
AbstractThe effects of interaction with phospholipids on the conformation of the alternating copolymer, poly(Leu‐Lys), and the random copolymer poly(Leu50, Lys50) have been investigated by CD and ir spectroscopy. Poly(Leu‐Lys) undergoes a partial unordered → β‐sheet transition in solution in the presence of lysolecithin. On addition of lysolecithin plus cholate, an unordered → α ‐helix transition is observed. In films deposited from these solutions, poly(Leu‐Lys) adopts the anti‐parallel β‐sheet conformation, as in aqueous solutions at moderate ionic strength. Polarized ir spectra showed that the plane of the β‐sheet in such films deviates from the plane of the film by no more than 14°. The random copolymer, poly(Leu50, Lys50), is α‐helical in the presence of lysolecithin and lysolecithin plus cholate, regardless of whether the sample is a solution or a film. CD measurements on the poly(Leu‐Lys) films provide information about the component of the CD tensor for light propagating normal to the plane of the β‐sheet. These measurements show (1) a negative n → π* CD band (214 nm maximum) with higher intensity than the average CD for isotropic solution; and (2) a positive band in the π → π* region (195 nm maximum), which is weaker than that in the isotropic spectrum.
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