Transmembrane orientation of reaction centers in proteoliposomes from Rhodopseudomonas sphaeroides

Koh Iba, Ken Ichiro Takamiya, Hiroyuki Arata, Yoshihiro Toh, Mitsuo Nishimura

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6 Citations (Scopus)


The photochemical reaction centers from Rhodopseudomonas sphaeroides were reconstituted with soybean phospholipids into liposomes by the cholate-dialysis method. The transmembrane orientation of the reaction centers in the proteoliposomes and the morphology of the vesicles were investigated. The orientastion was determined by the reduction of externally added cytochrome c after its photo-oxidation by a flash. The structure of the vesicles was examined by electron microscope.Discontinuous sucrose density gradient centrifugation yielded several proteoli-posome fractions with different vesicular sizes and reaction-center orientations. The proportion of the reaction centers that exposed their cytochrome c reacting sites to the outside of the vesicles increased from 45 to 85% with an increase of the vesicular size. The proportion also depended on the ionic composition of the dialysis buffer. The optimal ionic environment during the dialysis (100 mM NaCl or 2.5 mM MgSO4 gave a liposome yield of 25-30% with a highly asymmetric orientation (>60%). Entrapping of cytochrome c molecules into the phospholipid vesicles had little effect on the orientation of the reaction centers.

Original languageEnglish
Pages (from-to)1823-1830
Number of pages8
JournalJournal of biochemistry
Issue number6
Publication statusPublished - Oct 1984
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Molecular Biology


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