Infrared spectrum of the purple membrane: clue to a proton conduction mechanism?

The infrared spectrum of the purple membrane of Halobacterium halobium has amide I and amide A frequencies that are anomalously high for standard alpha-helical structures. Normal mode calculations indicate that these and other unusual features of the spectrum can be attributed to alpha 11-helices. Such structures suggest that the helix backbone may provide the framework through which proton transport takes place.