Quantitative Dissolution of the Membrane and Preparation of Photoreceptor Subunits from Rhodospirillum rubrum

Application of the alkaline-urea-Triton membrane dissolution procedure to membrane particles from Rhodospirillum rubrum has given results completely compatible with those previously obtained for Rhodopseudomonas spheroides. Phospholipid material is nearly completely displaced by Triton X-100 in the preparation of these particles. The average particle weight of the derived material is about 100,000 in 0.2 % Triton X-100 and the liberated photoreceptor subunits retain complete activity as measured by absorbance photochange, electron paramagnetic resonanee photochange, and the quantum yield for these processes. It is demonstrated that these fully active bacteriochlorophyll-trap-protein complexes are obtained in quantitative yield from the membrane with no significant change in spectral properties. Thus, together with earlier results with the R. spheroides system, these data strongly support the concept that photoreceptor subunits exist in the membrane along with other kinds of lipoprotein subunits. From preliminary analysis data it is shown that, of the transition metals present in the bacteria, only iron remains in these photoreceptor subunit preparations at a high enough concentration to play a role in the phototrap. The decrease in phototrap activity at lower potentials is measured and the results are shown to be consistent with an earlier suggestion which would assign this property to the primary electron acceptor molecule.