Purification of Cyanobacterial Thylakoid, Plasma, and Outer Membranes by Two-Phase Partitioning

Cyanobacteria, as gram-negative bacteria, are surrounded by a cell envelope consisting of the outer membrane and the plasma membrane with a peptidoglycan layer in between. However, cyanobacteria, is a unique prokaryote, because in addition to the cell envelope, there is an inner cytoplasmic membrane system-namely the chlorophyll-containing thylakoid membranes-which perform oxygenic photosynthesis, the most fundamental life process on the earth (1 ). This organism is also interesting from the evolutionary point of view, because it arose in a very ancient age and has survived in various environments. Furthermore, chloroplasts are believed to have evolved from cyanobacterial ancestors that developed an endosymbiotic relationship with an eukaryotic host cell.