Properties of oxygen-evolving photosystem-II particles from Phormidium laminosum, a thermophilic blue-green alga

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Abstract
O2-evolving photosystem[PS]-II particles from the thermophilic blue-green alga P. laminosum contained 1 mol Mn/13-17 mol chlorophyll a compared with 1 mol MN/65-75 chlorophyll a in unfractionated membranes. At least 2/3 of the Mn in the PS-II particles was removed by mild heating and by treatment with Tris or EDTA, with concomitant loss of O2 evolution. Irreversible inactivation was caused by washing in buffers without MgCl2 and this inactivation was not accompanied by a corresponding loss of Mn. Bivalent cations (Mg2+ or Ca2+), Cl- or Br- ions and at least 20% (vol/vol) glycerol were required for maximum stability of O2 evolution. The PS-II particles were enriched in high-potential cytochrome b-559 (1 mol cytochrome/50-60 mol chlorophyll a) and in component C-550 and had a photosynthetic-unit size of 40-70 molecules of chlorophyll a. The absorption spectrum at 77.degree. K showed a preponderance of shorter-wavelength forms of chlorophyll a in the PS-II particles and in the fluorescence emission spectrum at 77.degree. K there were major chlorophyll fluorescence bands at 684 nm and 695 nm, with almost no fluorescence in the far-red region. Analysis of the lipid and protein contents showed that the PS-II particles were not chemically pure (e.g., all membrane-bound cytochrome and cytochrome c-549 were present) but their high O2-evolution activity and good optical properties make them useful for functional studies on PS-II and O2 evolution.