Determination of the number of detergent molecules associated with the reaction center protein isolated from the photosynthetic bacterium Rhodopseudomonas viridis. Effects of the amphiphilic molecule 1,2,3-heptanetriol.

Detergent-free reaction center (RC) proteins from the photosynthetic bacterium Rhodopseudomonas viridis were obtained using Bio-Beads SM-2. With these RCs, the amount of detergent molecules associated with the protein was measured by determining the detergent concentration at which re-solubilization occurred as a function of the RC concentration. For N,N-dimethyl dodecylamine-N-oxide (LDAO), Triton X-100 and beta-octylglucoside 260 +/- 30,105 +/- 10 and 360 +/- 100 detergent molecules were necessary to dissolve the protein, respectively. With this technique we have studied the effect of the amphiphilic molecule 1,2,3-heptanetriol, which is essential in the crystallization process of these RCs. Addition of 5% 1,2,3-heptanetriol reduces the value for LDAO to 120 +/- 20 LDAO/RC, supporting the notion that crystallization of the RCs is promoted by increasing the number of protein-protein contacts.