Comparison of soluble and membrane polypeptides ofSynechocystis 6308 by two-dimensional electrophoresis

Abstract

Two-dimensional electrophoresis was carried out on fractions of the cyanobacteriumSynechocystis 6308 (ATCC 27150). Phycobilisomes isolated fromSynechocystis in 0.75M potassium phosphate buffer, pH 6.8, (KPi) plus Triton X-100 showed 5 prominent polypeptides when examined by two-dimensional electrophoresis. Ultracentrifugation of cells broken in KPi lacking Triton yielded three fractions, a membrane-containing pellet, a green supernatant, and a less dense yellow supernatant. The three fractions yielded a total of 272 polypeptides visualized by silver staining of two-dimensional gels. Fourteen polypeptides were found only in the yellow fraction, 14 polypeptides were found only in the green fraction, and 16 polypeptides were found only in the membrane fraction; 23 polypeptides were found in all three fractions. The crude Triton-containing KPi extract contained 62, and a 50 mM HEPES extract contained 55, of the 272 polypeptides visualized in these fractions. Two-dimensional electrophoresis combined with subcellular fractionation may be useful tools for examining changes in polypeptide composition caused by nitrogen starvation.