Electric Dichroism of Purple Membrane
The electric dichroism of bacteriorhodopsin has been studied by subjecting suspensions of purple membrane fragments (mean diameter ~ 0.5 µm) to pulsed electric fields. The reduced dichroism as a function of varying orientation of the purple membrane sheets was calculated, taking the P3 symmetry of the arrangement of bacteriorhodopsin molecules into account. The results for this symmetrical trimer model are different from those derived from the monomeric model used by others, showing that the latter underestimates the angle between the normal to the membrane plane and chromophore transition moment by several degrees. Analysis of the experiments in terms of the trimer model restricts the allowed transition moment orientations to either one or the other of two ranges of angles, according to whether the planes of the membrane fragments orient parallel or perpendicular to the imposed electric field.
KeywordsTransition Moment Membrane Fragment Linear Dichroism Purple Membrane Permanent Dipole Moment
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