Solubility diagram of the Rhodobacter sphaeroides reaction center as a function of PEG concentration

In order to quantify the effect of polyethylene glycol 4000 (PEG) on the solubility of an integral membrane protein, we have crystallized the photochemical reaction center from Rhodobacter sphaeroides Y by batch method on a large range of PEG. The measurement of the solubility diagram display a semi-logarithmic dependence of solubility versus PEG concentration. Comparison of our results with previously published ones [Odahara, T., Ataka, M. and Katsura, M. (1994) Acta Cryst. D50, 639–642] suggests a notable effect of additional 1,2,3-heptane-triol and/or temperature on photochemical reaction center solubility.