Molecular Organization of Photochemical Reaction Complex in Chromatophore Membrane from Rhodospirillum rubrum as Detected by Immunochemical and Proteolytic Analyses

The molecular organization of photochemical reaction (PR) complex in chromato-phores from Rhodospirillum rubrum was studied by a combination of proteolytic analysis with proteinase K followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunochemical analysis with rabbit polyclonal antibodies against its five subunits (H, M, L, α, and β). The preparations used for comparison were reaction center complex (RC) (composed of H, M, and L), PR complex, and chromatophores (closed membranous vesicles of polar lipid bilayer having PR complex buried in the membrane). 1. RC was bound with anti-H, anti-M, and anti-L antibodies, whereas PR complex and chromatophores were bound with anti-H and anti-β antibodies, but not with the other antibodies. 2. With PR complex, H (Mr 31,000 (3IK)) was rapidly degraded into two peptides with Mr of 16K and 14.5K (abbreviated as 16K and 14.5K, respectively), M (27K) into 25.5K, and β (11K) into 10K. Significantly later, the 25.5K of M was degraded into 24K, L (23K) into 19K, and α (12K) into llK. With chromatophores, H and β were degraded in a manner similar to that with PR complex, whereas M, L, and α were not degraded at all. With RC, H, M, and L were rapidly degraded. 3. With RC, the activity for photooxidation of P870 (photochemical activity) was hardly affected till H, M, and L had been degraded into < 10K, 24K, and 19K, respectively. With PR complex, the absorbance spectrum due to the bacteriochlorophylls of light-harvesting complex-1 composed of α and β (LH1-Bchl) changed in parallel to the degradation of α or .10K (a part of β). 4. Together with the previous results (Ueda et al. (1985) j. Biochem. 98, 1487-1498), the present findings suggest that: 1) RC is directly surrounded by 12 α and further by 12 β;2)H and β are mostly and partially exposed, respectively, on the outer surface of the membranous vesicle;3)a small part of M is exposed on the inner surface of the membranous vesicle.