A SEMIEMPIRICAL APPROACH FOR THE SIMULATION OF CIRCULAR-DICHROISM SPECTRA OF GRAMICIDIN-A IN A MODEL MEMBRANE

In an extension of our previous work (Bano, M. C., Braco, L., and Abad, C. 1991. Biochemistry. 30:886-94), the kinetics of dissociation of gramicidin A double-stranded dimers into beta-6.3-helical monomers in small unilamellar vesicles prepared following different protocols, were investigated using in combination circular dichroism (CD) and high-performance liquid chromatography (HPLC). The analysis of the data from both techniques according to a two-component model strongly supports that any given CD pattern of gramicidin incorporated in the phospholipid bilayer can be deconvoluted essentially as a linear combination of the reference subspectra calculated for the double-stranded dimer and the helical monomer. An HPLC-based, semi-empirical approach is proposed for the simulation of gramicidin CD curves in the model membrane used, and it is shown that the congruence between theoretical and experimental spectra is very satisfactory.