The Association of Different Detergents with the Photosynthetic Reaction Center Protein of Rhodobacter sphaeroides R26 and the Effects on its Photochemistry

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Abstract
Detergent‐free reaction centers from Rhodobacter sphaeroides R26 were used to study the solubilization of reaction centers in various detergents and their effects on reaction center photochemistry. 500 ± 100 n ‐octyl‐β‐d‐glucopyranoside or 51 ± 5 Triton X‐100 molecules were associated with one reaction center. For N,N‐alkylamine N‐oxide detergents with chain lengths in the range from 8–13 carbon atoms, the number of detergent molecules associated with the reaction centers increased with decreasing chain length. The amount of detergent molecules associated with the reaction centers decreased almost tenfold if the pH was increased from pH 6 to pH 10. The addition of 5% 1,2,3‐heptanetriol to various detergents lowered the detergent/reaction center ratio by a factor of two compared to that for the pure detergent. The detergent concentration at which solubilization of the reaction center occurs was close to the critical micelle concentration for all detergents studied. The absorption band at 865 nm of the primary donor in the reaction center shifts to 846 nm when detergent was removed from the reaction center; upon re‐solubilization with various detergents, this band shifts back to 865 nm. In 80–90% of the detergent‐free reaction centers, the secondary electron transfer from QA to QB was inhibited; this electron transfer was restored after re‐addition of detergent.

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