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Keywords:

  • dimmer;
  • photosynthesis;
  • photosystem II;
  • spinach;
  • structure

Abstract

  1. Top of page
  2. Abstract
  3. References

Membranes enriched in photosystem II were isolated from spinach and further solubilised using n-octyl β-d-glucopyranoside (OctGlc) and n-dodecyl β-d-maltoside (DodCl2). The OctGlc preparation had high rates of oxygen evolution and when subjected to size-exclusion HPLC and sucrose density gradient centrifugation, in the presence of DodGlc2, separated into dimeric (430 kDa), monomeric (236 kDa) photosystem II cores and a fraction containing photosystem II light-harvesting complex (Lhcb) proteins. The dimeric core fraction was more stable, contained higher levels of chlorophyll, β-carotene and plastoquinone per photosystem II reaction centre and had a higher oxygen-evolving activity than the monomeric cores. Their subunit composition was similar (CP43, CP47, DI, D2, cytochrome b 559 and several lower-molecular-mass components) except that the level of 33-kDa extrinsic protein was lower in the monomeric fraction. Direct solubilisation of photosystem-II-enriched membranes with DodGlc2, followed by sucrose density gradient centrifugation, yielded a super complex (700 kDa) containing the dimeric form of the photosystem II core and Lhcb proteins: Lhcbl, Lhcb2, Lhcb4 (CP29), and LhcbS (CP26). Like the dimeric and monomeric photosystem II core complexes, the photosystem II-LHCII complex had lost the 23-kDa and 17-kDa extrinsic proteins, but maintained the 33-kDa protein and the ability to evolve oxygen. It is suggested. with a proposed model, that the isolated photosystem II-LHCII super complex represents an in vivo organisation that can sometimes form a lattice in granal membranes of the type detected by freeze-etch electron microscopy [Seibert, M., DeWit, M. & Staehelin, L. A. (1987) J. Cell Biol. 105, 2257–22651.

Abbreviations
BBY

photosystein-II-enriched membranes isolated according to Berthold et al. (1981)

Chl

chlorophyll

CP

chlorophyll protein

CP43

product of the psbC gene

CP47

product of the psbB gene

cyt b 559

cytochrome b 559, consisting of the α (psbE gene product) and β- (psbF gene product) subunits

D1

product of the psbA gene

D2

product of thepsbD gene

DodGlc2

n-dodecy β-d-maltoside

ESs

exoplasmic (lumenal) surface in a stacked membrane region

OEC

oxygen-evolving complex

OctGlc

n-octyl β-D)-glucopyranoside

PQ

plastoquinone

PS

photosystem

LHC

light-harvesting complex

Lhcb

light-harvesting complex of photosystem II

References

  1. Top of page
  2. Abstract
  3. References