RESONANCE RAMAN STUDIES OF THE PHOTOCYCLE OF BACTERIORHODOPS IN: A MOLECULAR MECHANISM FOR PROTON PUMPING
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Date
1978
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Ohio State University
Abstract
Kinetic resonance Raman spectroscopy $techniques^{1}$ were employed to study the photocycle of the bacteriorhodopsin from the purple membrane of H. halobium. A suspension of purple membrane fragments in $H_{2} O$ and $D_{2} O$ at different pH values was flowed at variable speeds through a laser beam which triggers the photochemical event and is also used to excite the Raman scattering of the intermediate species produced. These studies indicate that there is a hitherto unknown intermediate, preceding the $M^{412}$ species. In these two species the Schiff-base linkage between the retinal chromophore and an $\in$-amino group of a lysine from the protein, is unprotonated, whereas in all the earlier intermediates this linkage is protonated. By tracing the intensity of Raman bands assigned to a protonated and unprotonated $Schiff-basea,^{2}$ we have shown that the rate of deprotonation is Increased at higher pH and exhibits a pH value of 10.2. This suggests that a second lysin from the protein interacts with the Schiff base linkage. Based on this and other results we propose a molecular mechanism for the proton pumping across the membrane which occurs during the photo-cycle of bacteriorhodopsin.
Description
$^{1}$M. Marcus and A. Lewis, Science 195, 1932 (1977). $^{2}$A. Lewis, J. Spoonhower, R. A. Bogomolni, R.H. Lozier and W. Stoeckenius, Proc. Nat. Acad. Sci. U.S.A. 71, 4462 (1974).""
Author Institution: School of Applied and Engineering Physics, Cornell University
Author Institution: School of Applied and Engineering Physics, Cornell University