Isolation and characterization of oxygen-evolving thylakoid membranes and photosystem II particles from a glaucocystophyte, Cyanophora paradoxa

Conditions for preparing oxygen-evolving thylakoid membranes and PSII compl exes, and those for observing the PSII activity were investigated in a glau cocystophyte, Cyanophora paradoxa. The active thylakoid membranes were isol ated either with a medium containing glycerol or with that containing high concentrations of sucrose, phosphate, and citrate, Active PSII particles we re solubilized by octyl-beta -D-glucoside from thylakoid membranes and were separated by sucrose density gradient centrifugation, The thylakoid membra nes and PSII particles showed an oxygen-evolving activity only in high-ioni c-strength media. The extrinsic 33 kDa protein (PsbO) and the cytochrome c( 550) (PsbV) were found to be present in the PSII particles as in cyanobacte ria or red algae, but no 12 kDa protein (PsbU) was detected, The PsbO prote in was classified as a land-plant type by its N-terminal amino acid sequenc e.