Composition of a photosystem I chlorophyll protein complex from Anabaena flos-aquae

The use of Triton X-100 to solubilize membrane fragments from Anabaena flos-aquae in conjunction with DEAE cellulose chromatography allows the separation of three green fractions. Fraction 1 is detergent-solubilized chlorophyll, and Fraction 2 contains one polypeptide in the 15 kdalton area. Fraction 3, which contains most of the chlorophyll and shows P-700 and photosystem I activity, shows by SDS gel electrophoresis varying polypeptide profiles which reflect the presence of four fundamental bands as well as varying amounts of other polypeptides which appear to be aggregates containing the 15 kdalton polypeptide. The four fundamental bands are designated Band I at 120, Band II at 52, Band III at 46, and Band IV at 15 kdaltons. Band I obtained using 0.1% SDS contains chlorophyll and P-700 associated with it. When this band is cut out and rerun, the 120 kdalton band is lost, but significant increases occur in the intensities of Bands II, III, and IV as well as other polypeptides in the 20-30 kdalton range. The use of 1% Triton X-100 coupled with sucrose density gradient centrifugation allows the separation of three green bands at 10, 25 and 40% sucrose. The 10% layer contains a major polypeptide which appears to be Band IV. The 25 and 40% layers show essentially similar polypeptide profiles, resembling Fraction 3 in this regard, except that the 40% layer shows a marked decrease in Band III. Treatment of the material layering at the 40% sucrose level with a higher (4%) concentration of Triton X-100 causes a loss (disaggregation) of the polypeptides occurring in the 60-80 kdalton region and in increase in the lower molecular weight polypeptides. Thus, aggregation of the lower molecular weight polypeptides accounts for the variability seen in the electrophoresis patterns. Possible relations of the principal polypeptides to the known photochemical functions in the original membrane are discussed.