Properties of the Photosynthetic System and DNA of Cyanophora paradoxa Cyanelles

The cyanelle from the photosynthetic biflagellate protist Cyanophora paradoxa has been studied in terms of its photosynthetic properties. Structurally, the cyanelle resembles unicellular cyanobacteria. The cyanelle is readily released from the host cell by means of the French press. The isolated cyanelle shows typical photosystem I and photosystem II activities as well as phenazine methosulfate-mediated photophosphorylation. The kinetic parameters Km and Vmax were determined for CO2 fixation in the cyanelle and cells of C. paradoxa and compared to a cyanobacterium. The determined values were not much different, although the cyanobacterium had a significantly greater rate of CO2 fixation, and the cyanelle was least active in this regard. Photosystem I chlorophyll-protein complex is readily isolated from the thylakoid membrane. In all these respects, the photosynthetic apparatus of the cyanelle resembles that of cyanobacteria. No nitrogen fixation activity was observed. Attempts to regenerate the isolated cyanelle were not successful, but in some cases, an unidentified cyanobacterium grew up in standing cultures of C. paradoxa cyanelles. Buoyant density data indicate that the strain of C. paradoxa we have investigated differs from that employed by others, since our strain shows a value of 1.716 grams per cubic centimeter and others report values of 1.695 and 1.691.