A FRACTION FROM ANABAENA VARIABILIS ENRICHED IN REACTION CENTER CHLOROPHYLL P700

Extraction of carotenoids from lyophilized membrane fragments of Anabaena variabilis followed by treatment with Triton X-100 and sucrose density gradient centrifugation yields a bluish-green membrane fragment which is enriched in P700. This high-P700 fragment, denoted HP700, contains three P700 molecules per 100 chlorophyll a; the ratio is three times higher than that of the Photosystem I fragment (obtained by treatment with Triton X-100 alone). Examination of the HP700 fragment by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate reveals the presence of only one chlorophyll-protein complex band. The protein content in the HP700 fragment is about half that of the Photosystem I fragment on a chlorophyll a basis. The HP700 fragment shows the characteristic absorbance change of P700 and the related electron paramagnetic resonance signal upon illumination. Compared with the Photosystem I fragment, the HP700 fragment shows a slower rate of bleaching of P700 upon illumination. These two fragments also differ in their fluorescence properties. The intensity of fluorescence at 685 mμ is higher for the HP700 fragment at 25°. At -196° the long-wavelength fluorescence is found at a shorter wavelength (722 mμ) in the HP700 fragment and is lower in intensity than that observed with the Photosystem I fragment. These data indicate that there is less efficient energy transfer between the light-harvesting chlorophyll a and P700 in the HP700 fragment. The electron micrograph of the HP700 fragment shows the presence of small membrane fragments and some strands. Exposure of the HP700 fragment to ferricyanide or to light causes an oxidation of the P700 chlorophyll. Accompanying this change is a decrease in absorbance at 680 mμ. This change may represent another chlorophyll species which is part of the reaction center complex. © 1969.