title: Circular dichroism of heterochromophoric and partially regenerated purple membrane: search for exciton coupling.
abstract: In order to determine the origin of the bisignate CD spectra of native purple membrane, heterochromophoric analogues containing bacteriorhodopsin regenerated with native all-trans-retinal and retinal analogues were investigated. The data collected for the purple membrane samples containing two different chromophores suggest the additive character of the CD spectra. This conclusion was supported by a series of spectra using 5,6-dihydroretinal and 3-dehydroretinal and by using 33% regenerated PM in buffer and in presence of osmolytes. Our results support the idea of conformational heterogeneity of the chromophores in the bR in the trimer, suggesting that the three bR subunits in the trimer are not conformationally equal, and therefore, the bisignate CD spectrum of bR in the purple membrane occurs rather due to a superposition of the CD spectra from variously distorted bR subunits in the trimer than interchromophoric exciton-coupling interactions.
authors.affiliation: Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, MD 20892, USA.
authors.forename: Elena
authors.initials: E
authors.lastname: Karnaukhova
authors.forename: Chrysoula
authors.initials: C
authors.lastname: Vasileiou
authors.forename: Andy
authors.initials: A
authors.lastname: Wang
authors.forename: Nina
authors.initials: N
authors.lastname: Berova
authors.forename: Koji
authors.initials: K
authors.lastname: Nakanishi
authors.forename: Babak
authors.initials: B
authors.lastname: Borhan
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry; D002942:Circular Dichroism / Q000379:methods*; D003593:Cytoplasm / Q000378:metabolism; D019281:Dimerization; D006217:Halobacterium / Q000378:metabolism; D025602:Halorhodopsins / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D018717:Purple Membrane / Q000378:metabolism* / Q000648:ultrastructure; D012172:Retinaldehyde / Q000737:chemistry; D013237:Stereoisomerism; D013395:Sucrose / Q000737:chemistry; D014466:Ultraviolet Rays
chemical_list: D025602:Halorhodopsins; D001436:Bacteriorhodopsins; D013395:Sucrose; D012172:Retinaldehyde