title: Polarized infrared spectroscopy of oriented purple membrane.
abstract: 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.
mesh_terms: 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
chemical_list: D002338:Carotenoids; D001436:Bacteriorhodopsins
references.citation: J Mol Biol. 1962 Jun;4:528-40
references.pmid: 14459672
references.citation: J Mol Biol. 1977 Dec 15;117(3):607-20
references.pmid: 609098
references.citation: Biochem J. 1977 Apr 1;163(1):45-57
references.pmid: 869919
references.citation: Science. 1977 Mar 25;195(4284):1328-30
references.pmid: 841330
references.citation: Biophys J. 1976 Oct;16(10):1183-200
references.pmid: 963198
references.citation: Nat New Biol. 1971 Sep 29;233(39):152-5
references.pmid: 5286750
references.citation: Science. 1976 Mar 19;191(4232):1176-8
references.pmid: 1257742
references.citation: J Mol Biol. 1975 Apr 5;93(2):123-38
references.pmid: 239244
references.citation: Biochem Biophys Res Commun. 1975 Jan 2;64(3):1054-61
references.pmid: 238520
references.citation: Proc Natl Acad Sci U S A. 1973 Oct;70(10):2853-7
references.pmid: 4517939
references.citation: Proc Natl Acad Sci U S A. 1974 Nov;71(11):4462-6
references.pmid: 4530995
references.citation: J Supramol Struct. 1974;2(5-6):769-74
references.pmid: 4461852
references.citation: Chem Phys Lipids. 1975 Nov;15(2):222-42
references.pmid: 1204133
references.citation: J Mol Biol. 1975 Apr 5;93(2):139-58
references.pmid: 1152049
references.citation: J Mol Biol. 1975 Feb 15;92(1):1-13
references.pmid: 1152039
references.citation: Nature. 1975 Sep 4;257(5521):28-32
references.pmid: 1161000
references.citation: Prep Biochem. 1975;5(2):161-78
references.pmid: 1144313
references.citation: Can J Biochem. 1975 Mar;53(3):284-92
references.pmid: 1125815
references.citation: Biochim Biophys Acta. 1968 Mar 1;150(2):186-93
references.pmid: 5689246
references.citation: Science. 1968 Apr 19;160(3825):314-6
references.pmid: 5641262
references.citation: J Biol Chem. 1967 Dec 10;242(23):5467-73
references.pmid: 12325361
references.citation: J Biol Chem. 1967 Dec 10;242(23):5460-6
references.pmid: 12325360