This paper investigates the fast photocurrent components, B1 and B2, from oriented bacteriorhodopsin (BR) membrane films at low pH, under pulsed laser excitation. Adding chloride ion changes the acid-blue BR to its acid-purple form. In the presence of chloride, the acid-purple BR shows a positive B2 component in the same direction as that of BR at neutral pH, indicating a rapid intramolecular charge transfer. In the absence of chloride, the acid-blue BR shows only a negative B1 with multi-components, indicating a rapid charge separation process associated with retinal photoisomerization. The multi-components in B1 are possibly formed due to the heterogeneity of the acid-blue BR. In addition, BR mutants, D85N and D115N, at low pH and in the presence of chloride, generate the B2 component as well. The observation of chloride-dependent B2 component in various cases at low pH, is in favor of a possible transient chloride ion transfer, although the nature of the charge being transferred cannot be identified so far.
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1 April 2000
Photocurrent from Oriented Membrane Films Containing Acid-blue and Acid-purple Bacteriorhodopsin and its Mutants
Jianping Wang
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Photochemistry and Photobiology
Vol. 71 • No. 4
April 2000
Vol. 71 • No. 4
April 2000