Solubilization of green plant thylakoid membranes with n-dodecyl-alpha,D-maltoside. Implications for the structural organization of the Photosystem II, Photosystem I, ATP synthase and cytochrome b(6)f complexes

A biochemical and structural analysis is presented of fractions that were o btained by a quick and mild solubilization of thylakoid membranes from spin ach with the non-ionic detergent n-dodecyl-alpha ,D-maltoside, followed by a partial purification using gel filtration chromatography. The largest fra ctions consisted of paired, appressed membrane fragments with an average di ameter of about 360 nm and contain Photosystem II (PS II) and its associate d light-harvesting antenna (LHC II), but virtually no Photosystem I, ATP sy nthase and cytochrome b(6)f complex. Some of the membranes show a semi-regu lar ordering of PS II in rows at an average distance of about 26.3 nm, and from a partially disrupted grana membrane fragment we show that the superco mplexes of PS II and LHC II represent the basic structural unit of PS II in the grana membranes. The numbers of free LHC II and PS II core complexes w ere very high and very low, respectively. The other macromolecular complexe s of the thylakoid membrane occurred almost exclusively in dispersed forms. Photosystem I was observed in monomeric or multimeric PS I-200 complexes a nd there are no indications for free LHC I complexes. An extensive analysis by electron microscopy and image analysis of the CF0F1 ATP synthase comple x suggests locations of the delta (on top of the F-1 headpiece) and epsilon subunits (in the central stalk) and reveals that in a substantial part of the complexes the F-1 headpiece is bended considerably from the central sta lk. This kinking is very likely not an artefact of the isolation procedure and may represent the complex in its inactive, oxidized form.