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HPLC purification of a biologically active membrane protein: the reaction center from photosynthetic bacteria.

Reaction centers from Rhodopseudomonas sphaeroides R 26 have been isolated from a crude extract obtained by lauryldimethylamine oxide extraction of chromatophore membranes, by HPLC using a combination of surface-mediated and size exclusion chromatography. The eluted RCs exhibit a normal activity (t 1/2 of the back-reaction is 70 ms) and are recovered in good yield (over 50% based on the activity) and purity (based on the A 280 nm/A 800 nm = 1.30 +/- 0.05 ratio and the characteristic 3 polypeptides SDS-PAGE pattern). The elution time (5-10 mn) is about two orders of magnitude faster than for the classical purification techniques.

Bacterial Proteins↗

Structure of a bacterial photosynthetic membrane: integrity of reaction centers following proteolysis and detergent solubilization.

The photosynthetic membranes of the purple bacterium Rhodopseudomonas viridis are composed of a semi-crystalline lattice of subunits. Proteolysis of isolated membranes with trypsin or pronase results in the degradation of polypeptides associated with the photosynthetic reaction center. However, two low molecular weight peptides which may form the light-harvesting complex survive the enzymatic treatment. The proteolysis does not affect the major absorbance peak (830 nm) associated with the reaction center. However, treatment of proteolyzed membranes with detergents such as LDAO abolishes the 830 nm absorbance peak. The 830 nm peak is stable following LDAO solubilization of non-proteolyzed membranes. These results suggest that a combination of covalent and non-covalent interactions are important in maintaining the configuration of the reaction center, and are consistent with a model of membrane organization in which the light-harvesting components are buried in a lipid phase of the membrane and reaction center components form the large structures which electron microscope studies have shown to extend from either membrane surface.

Bacterial Proteins↗