Preparation and characterization of Photosystem II particles from a thermophilic cyanobacterium

Abstract

Photosystem II particles have been isolated and purified from the thermophilic cyanobacterium Mastigocladus laminosus after sulfobetaine treatment. The light-induced steady-state electron transport, flash-induced absorption changes at 830 nm and 325 nm, reflecting the turnover of P-680 and of the acceptor side, respectively, have been measured. In the presence of artificial electron acceptors the preparations showed high O 2-evolution activities (e.g., 3000–4000 μmol O 2 per mg Chl a per h with phenyl- p-benzoquinone) which were DCMU-sensitive. O 2-evolution activity was stable in the presence of various cations (10 mM) and of glycerol (25% (v/v) in the suspending medium. Furthermore, the activity was stable up to 60°C and maximum rate of the electron transport was observed at 50°C. The spectrum of the particles showed a chlorophyll a maximum at approx. 673 nm, some carotenoids were still present but phycocyanin was completely removed. After SDS-polyacrylamide gel electrophoresis the preparations contained mainly nine protein bands at 110, 105, 60, 55, 35, 33, 22, 18 and 17 kDa. Under repetitive laser flash excitation the P-680 +-reduction kinetics contained components in the nanosecond and microsecond range with an absorption rate of approx. 1:1. When PS-II particles were purified at room temperature by anion-exchange chromatography nanosecond relaxation kinetics were observed even though the particles did not evolve oxygen. The gel analysis for this preparation showed mainly four protein bands at 60, 55, 35 and 18 kDa.