Evidence for the existence of trimeric and monomeric Photosystem I complexes in thylakoid membranes from cyanobacteria
✍ Scribed by Jochen Kruip; Dirk Bald; Egbert Boekema; Matthias Rögner
- Publisher
- Springer
- Year
- 1994
- Tongue
- English
- Weight
- 876 KB
- Volume
- 40
- Category
- Article
- ISSN
- 0166-8595
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✦ Synopsis
In cyanobacteria, solubilization of thylakoid membranes by detergents yields both monomeric and trimeric Photosystem I (PS I) complexes in variable amounts. We present evidence for the existence of both monomeric and trimeric PS I in cyanobacterial thylakoid membranes with the oligomeric state depending 'in vitro' on the ion concentration. At low salt concentrations (i.e.≤10 mM MgSO4) PS I is mainly extracted as a trimer from these membranes and at high salt concentrations (i.e.≥150 mM MgSO4) nearly exclusively as a monomer, irrespective of the type of salt used (i.e. mono- or bivalent ions) and the temperature (i.e. 4°C or 20°C). Once solubilized, the PS I trimer is stable over a wide range of ion concentrations (i.e. beyond 0.5 M). A model is presented which suggests a monomer-oligomer equilibrium of PS I, but also of PS II and the cyt. b6/f-complex in the cyanobacterial thylakoid membrane. The possible physiological role of this equilibrium in the regulation of state transitions is discussed.