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REVIEW: Importance of Lipids for Bacteriorhodopsin Structure, Photocycle, and Function

R. W. Hendler1* and S. Dracheva1,2

1Laboratory of Cell Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, 20892, USA; fax: 301-402-1519; E-mail: rwh@helix.nih.gov

2Present address: National Center for Biotechnology Information, National Library of Medicine, NIH, Bethesda, Maryland, USA

* To whom correspondence should be addressed.

Received April 11, 2001; Revision received May 24, 2001
This review begins with a brief history of early studies on the involvement of lipids in certain bacteriorhodopsin (BR) properties. Such properties include the regulation of the pK for the purple to blue transition caused by deionization, and the reformation of trimers from monomers after exposure of the purple membrane to Triton X-100. Most of the review is devoted to newer studies which indicate an important role for the neutral lipid squalene in the functional stability of the fast-decaying M-intermediate, for its decay through a pathway involving the O-intermediate, and for the regulation of the relative amounts of slow-decaying and fast-decaying forms of M. Participation of a peripheral acidic amino acid in the overall expression of fast-decaying M is also discussed. Initial studies suggest that the acidic amino acid may be Asp36 and/or Asp38.
KEY WORDS: bacteriorhodopsin, lipids, photocycle, Triton X-100, purple membranes, reconstitution