Electron microscopy of the poly-L-lysine alpha-helix.

Dark field electron micrographs of polylysine molecules in the alpha-helical form were analyzed by digital Fourier techniques to determine the extent to which the helix was still represented in the images. A total of 50 molecular images were selected following defined criteria, 13 from spreads of molecules from aqueous solution and 37 from methanol solution. As controls, similar shapes were chosen from the random structure seen in the carbon specimen support without polylysine. Computer analysis of the 50 molecular images indicated the presence of a helical structure with a pitch of 0.54 +/- 0.01 nm and a pitch angle of 25.6 degrees +/- 1.5 degrees (standard error) in over 70% of the images. Moreover, 63% of the total alpha-helix measured by circular dichroism for the molecules in solution was still represented in the micrographs. The controls had no helical characteristics.