THE ASSOCIATION OF DIFFERENT DETERGENTS WITH THE PHOTOSYNTHETIC REACTION-CENTER PROTEIN OF RHODOBACTER-SPHAEROIDES R26 AND THE EFFECTS ON ITS PHOTOCHEMISTRY

Detergent-free reaction centers from Rhodobacter sphaeroides R26 were used to study the solubilization of reaction centers in various deterg ents and their effects on reaction center photochemistry. 500 +/- 100 n-octyl-beta-D-glucopyranoside or 51 +/- 5 Triton X-100 molecules were associated with one reaction center. For N,N-alkylamine N-oxide deter gents with chain lengths in the range from 8-13 carbon atoms, the numb er of detergent molecules associated with the reaction centers increas ed with decreasing chain length. The amount of detergent molecules ass ociated with the reaction centers decreased almost tenfold if the pH w as 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 fur the pure detergent. The detergent concentration at which solubilization of the reaction center occurs w as close to the critical micelle concentration for all detergents stud ied. The absorption band at 865 nm of the primary donor in the reactio n center shifts to 846 nm when detergent was removed from the reaction center; upon resolubilization with various detergents, this band shif ts back to 865 nm. In 80-90% of the detergent-free reaction centers, t he secondary electron transfer from Q(A) to Q(B) was inhibited; this e lectron transfer was restored after re-addition of detergent.