ASSOCIATION OF LHI-ALPHA(B870) POLYPEPTIDE WITH PHOSPHOLIPIDS DURING INSERTION IN THE PHOTOSYNTHETIC MEMBRANE OF AN LHII(-) MUTANT OF RHODOBACTER-CAPSULATUS

Membranes from in vivo labeled cells of Rhodobacter capsulatus U43[pTX 35] grown photosynthetically carried 60% of the [P-32]-Pi in the ''hea vy'' fraction (HM) after sucrose gradient sedimentation, Metal-chelati ng chromatography of either ''heavy'' or ''Light'' (LM) membrane fract ions rendered similar Bchl-protein complex profiles after octyl-glucos ide treatment, including most of the radioactivity in the same corresp onding elution fraction (F II). Similar labeling distribution of pigme nt-protein complexes was obtained for membranes of dark-grown cells in duced by lowering oxygen tension. Fractions derived from HM showed hig hly labeled LHI alpha, whereas the same complex from LM was essentiall y [P-32]-Pi-free, as revealed by SDS PAGE followed by autoradiography. Phospholipid analysis showed a similar pattern for membranes isolated from cells photosynthetically or semiaerobically grown, being the mos t abundant: phosphatidyl glycerol, phosphatidylethanolamine, cardiolip in, and phosphatidyl-choline. Part of the phospholipids from HM comigr ated with LHI alpha during SDS-PAGE and dissociated from the complexes only after solvent extraction and hydrophobic chromatography, However , a small amount remained always attached to LHI alpha, indicating an unusual strong interaction. These results suggest the existence of two operationally defined membrane regions carrying LHI alpha complexes d iffering in phosphorylation status and protein-phospholipid interactio n.