Angular orientation of the retinyl chromophore of bacteriorhodopsin: Reconciliation of2H NMR and optical measurements

Bruce S. Hudson

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


It is argued on the basis of MNDO - PSDCI calculations that, at the wavelength of electronic dichroism studies used to infer structure, the transition dipole moment of the retinyl Schiffs base chromophore of bacteriorhodopsin makes an angle of 10.5 ± 3.5° with respect to the long axis of the chromophore. The magnitude and direction of this off-axis angle helps to reconcile the differences between the deuterium NMR and optical determinations of the angular orientation of the chromophore in bacteriorhodopsin. Reconciliation of the NMR and optical dichroism structures is only possible, however, when the chromophore is oriented so that the imine proton points toward the extracellular surface. After correction, the published electronic dichroism data predict a chromophore angle of Q = 61 ± 7°, where Ω is defined as the angle of a line connecting chromophore atoms C5 and C15 relative to the membrane normal. The corresponding NMR results are Ω = 53.7 ± 4.1°. The combined data with equal weighting yield Ω = 57 ± 8°. This estimate is smaller than Ω = 70.6 ± 3.2° derived from recent diffraction studies, and the possible origins of these differences are discussed.

Original languageEnglish (US)
Pages (from-to)2274-2281
Number of pages8
JournalJournal of Physical Chemistry A
Issue number14
StatePublished - Dec 1 1999

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry


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