Abstract
Thermo- and acido-phylic primitive red alga, Cyanidioschyzon merolae, is considered to be one of the most primitive eukaryotic oxygenic photoautotrophs. We investigated the biochemical characteristics of photosystem II ( PSII ) complexes in C. merolae. The PSII complexes, retaining high oxygen-evolving activity, were purified as monomeric and dimeric forms. The chlorophyll a specific yield of purified PSII monomer plus dimer was approximately 20% based on the initial solubilaized thylakoid membrane. The proportion of the purified PSII complexes was approximately 1 monomer to 4 dimers. Both of the monomer and dimer were consisted of over 17 subunits, including PsbO, PsbQ, PsbU, PsbV, and Psb30 ( Ycf12 ). The composition of pigments and quinone was the same as that of the PSII complexes from a cyanobacterium, Thermosynechococcus elongatus. These results indicate that the PSII complex in C. merolae is similar to that in cyanobacteria rather than that in green plants.
