Polarized infrared spectroscopy of oriented purple membrane.
Polarized Fourier transform infrared spectroscopy has been used to study the structure of purple membrane from Halobacterium halobium. Membranes were oriented by drying a suspension of membrane fragments onto Irtran-4 slides. Dichroism measurements of the amide I, II and A peaks were used to find the average spatial orientation of the bacteriorhodopsin alpha-helices. By deriving a function that relates the observed dichroism to the orientational order parameters for the peptide groups, helical axis distribution, and mosaic spread of the membranes, the average orientation of the alpha-helices was found to lie in a range of less than 26 degrees away from the membrane normal, agreeing with electron microscopic measurements. The frequency of the amide I and A peaks is at least 10 cm-1 higher than values found for most alpha-helical polypeptides and proteins. This may indicate that bacteriorhodopsin contains distorted alpha-helical conformations.
D001436:Bacteriorhodopsins; D002338:Carotenoids; D002942:Circular Dichroism; D005583:Fourier Analysis; D006217:Halobacterium / Q000032:analysis; D008433:Mathematics; D008954:Models, Biological; D011487:Protein Conformation; D013055:Spectrophotometry, Infrared
D002338:Carotenoids; D001436:Bacteriorhodopsins
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