title: Counter-current distribution of sonicated inside-out thylakoid vesicles.
abstract: Inside-out thylakoid vesicles were isolated from spinach chloroplasts, and fragmented by sonication. Different fragments were separated by counter-current distribution and analyzed for chlorophyll and P700. The inside-out vesicles had a chlorophyll a/b ratio of 2.2-2.4 (original chloroplasts 2.8-3.0). After further fragmentation of the inside-out vesicles by sonication and separation by countercurrent distribution three populations of vesicles were obtained having chlorophyll a/b ratios of 1.7, 1.9 and 2.5 respectively. The P-700 was depleted in fractions with lower chlorophyll a/b ratio and was nearly absent in the fraction having a chlorophyll a/b ratio of 1.7 (chlorophyll/P700 greater than 4500 mol/mol). That PSII membrane vesicles, with such a low chlorophyll a/b ratio and lacking PSI, can be prepared by a non-detergent method provides strong support for the notion that PSI and PSII are segregated along the thylakoid membrane. A plot of P700 per chlorophyll against chlorophyll b/(a + b) fits a straight line connecting the pure PSI membrane (chlorophyll a/b = 6; P700/chlorophyll = 5.6 mmol/mol) with the pure PSII membrane (chlorophyll a/b = 1.7; P700 = 0). These two membranes can be considered as separate phases of a two-dimensional phase system. Models for the thylakoid membrane are discussed.
authors.affiliation: Department of Biochemistry, University of Lund, Sweden.
authors.forename: P A
authors.initials: PA
authors.lastname: Albertsson
authors.forename: P
authors.initials: P
authors.lastname: Svensson
mesh_terms: D002736:Chloroplasts / Q000032:analysis*; D003377:Countercurrent Distribution; D007425:Intracellular Membranes / Q000032:analysis; D013010:Sonication; D013347:Subcellular Fractions; D014675:Vegetables / Q000032:analysis