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. 1986 Dec;83(23):8972–8976. doi: 10.1073/pnas.83.23.8972

Stoichiometric model of the photosynthetic unit of Ectothiorhodospira halochloris

Harald Engelhardt *, Andreas Engel †, Wolfgang Baumeister *
PMCID: PMC387056  PMID: 16593781

Abstract

A stoichiometric model of the photosynthetic unit of Ectothiorhodospira halochloris has been obtained by means of scanning transmission electron microscope mass determination and mass mapping in conjunction with polyacrylamide gel electrophoresis. One reaction center, consisting of four single polypeptides, including one cytochrome, is surrounded by six identical light-harvesting complexes, each containing three polypeptides with 2:2:2 stoichiometry. This stoichiometric model was incorporated into the three-dimensional structure of the photosynthetic unit as derived from surface relief reconstructions of the two surfaces of shadowed membranes. The reaction center protrudes substantially from both membrane surfaces and has the cytochrome attached to the periplasmic face in a noncentrosymmetric fashion. The reaction center may assume various orientations within the photosynthetic complexes.

Keywords: mass mapping, scanning transmission electron microscopy, image processing, three-dimensional reconstruction, bacterial photosynthetic membrane

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