Occurrence of a Photosystem II polypeptide in non-photosynthetic membranes of cyanobacteria

Cytoplasmic and thylakoid membranes have been purified from the cyanobacteria Anacystis nidulans R2 and Phormidium laminosum by sucrose density gradient centrifugation. Probing of Western blots of proteins from these purified membrane fractions with antibodies directed against the 33 kDa polypeptide of Photosystem II from pea indicates that this protein is present in both the thylakoid and cytoplasmic membranes, rather than just the thylakoid membranes. This has been confirmed by immunogold labelling of cells. Oxygen evolution assays have been used to show that the 33 kDa polypeptide is not assembled into a functional Photosystem II complex in the cytoplasmic membranes. This may be due to the absence of other Photosystem II components.