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The Photocycle of Bacteriorhodopsin in the Two-Dimensional Orthorombic Crystal Form of Purple Membrane

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Michel,  Hartmut
Max Planck Institute of Biochemistry, Max Planck Society;

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Citation

Korenstein, R., Michel, H., & Hess, B. (1985). The Photocycle of Bacteriorhodopsin in the Two-Dimensional Orthorombic Crystal Form of Purple Membrane. Biophysical Journal, 47(3), 295-302. doi:10.1016/S0006-3495(85)83919-9.


Cite as: http://hdl.handle.net/21.11116/0000-0006-F373-6
Abstract
Laser flash photolysis and low-temperature absorption studies of the photocycle of orthorhombic purple membrane (o-PM) reveal the existence of the same K, L, and M intermediates as found in the native hexagonal purple membrane (h-PM). However, the 0 intermediate is missing in the o-PM. The absorption spectrum of the K intermediate of o-PM is blueshifted by ∼15 nm relative to the K intermediate found in the hexagonal purple membrane. The decay relaxation time constants of M in the o-PM are higher by more than an order of magnitude than the corresponding relaxation time constants in the h-PM. Similarly to the h-PM, the decay of M depends on the pulse width of excitation. The time-independent anisotropy factor obtained in photoselection studies of the M intermediate demonstrates the complete immobility of bacteriorhodopsin (bR) within the o-PM matrix. The same anisotropy factor of 0.3 obtained for o-PM and for h-PM suggests that in both crystalline lattices the transition moment of the retinal chromophore has similar angles with the plane of the membrane. The dependence of the decay kinetics of M on its occupancy may suggest the existence of kinetic coupling between neighboring bR molecules