Photosystem 2 of anacystis nidulans

Abstract

The main objective of this work was to prepare and characterise an oxygen-evolving Photosystem 2 particle, isolated from thylakoid membranes of the cyanobacterium, Anacystis nidulans.
Ihylakoid membranes were prepared by disrupting the cell-wall in a French pressure apparatus, follo.-Jed by differential centrifugation. 'Ihe ability to produce oxygen-evolving thylakoid membranes was determined by two factors, (a) the use of freshly harvested whole cells grown to late logarithmic phase and (b) the presence of glycerol and calcium in the cell-breakage buffer.
Photosystem 2 particles enriched in oxygen-evolution were prepared by extraction of the thylakoid membranes with lauryldimethyl­amine oxide, followed by sucrose density gradient centrifugation.
'Ihe particles demonstrated typical rates >300 µmoles 02.rtgCl'lla-1 .hr-1 with ferricyanide as electron acceptor. Cytochrome b559 was present in the PS2 particles in amounts of about 1 mol. cytochrome:83 mol. Chlorophyll a. Photosystem 1 particles were also prepared during the same extraction procedure and had typical P700:Cl'llorophyll a molar ratios of about 1:106.
'Ihe PS1 and PS2 particles were enriched in chlorophyll-protein ccmplexes compared with thylakoid membranes. 'Ihe chlorophyll­ protein complex of lowest mobility contained one major polypeptide at 60 Kd and a P700:Chla ratio of about 1:60. 'Ihe chlorophyll protein complex of higher mobility contained two major polypeptides at 40 and 46 Kd and no detectable P700.
Calcium was shown to be a specific requirement for the isolation of oxygen-evolving PS2 particles and in the absence of calcium, particles with very low rates of oxygen-evolution were obtained.
This was related to a substantial decrease in polypeptides at 30, 33 and 36 Kd.
Alkaline Tris-treatment of PS2 particles released