ISOLATION AND CHARACTERIZATION OF THE PLASMA-MEMBRANE BY 2-PHASE PARTITIONING FROM THE ALKALOPHILIC CYANOBACTERIUM SPIRULINA-PLATENSIS

Partition in aqueous dextran-polyethylene glycol two-phase system was used to isolate the plasma membranes from the alkalophilic cyanobacter ium Spirulina platensis. The upper phase contained a colorless membran es obtained in relatively short time, 3-4 h. This fraction had a diffe rent protein profile than that of the thylakoid fraction obtained in t he lower phase. It did not contain cytochrome c-oxidase activity, but retained characteristic Mg2+-ATPase activity that is sensitive to vana date, stimulated by K+, and has a pH optimum near 8.5. These data supp ort our assumption that the upper phase of the gradient consist of the plasma membrane of S. platensis.