Chemical and functional studies on the importance of purple membrane lipids in bacteriorhodopsin photocycle behavior

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Abstract
In native purple membrane (PM), there are approximately 1 squalene, 2 glycolipid sulfate (GLS), and 6 phospholipid (PL) molecules per bacteriorhodopsin (BR) monomer [10]. Brief (∼ 2 min) exposure to 0.1% Triton X‐100 removes about 25%, 20%, and 6% of squalenes, GLS, and PL, respectively (this paper) while causing profound changes in the BR photocycle, including the loss of ‘photocooperativity’ [1]. The BR photocycle in Triton‐treated PM can be restored to near normal behavior by reconstitution with native PM lipids. Isolated squalenes are not effective whereas PL alone partially restores normal photocycle characteristics.