Photosynthetic Activities of Membrane Preparations of the Blue‐Green Alga Phormidium luridum

Techniques have been developed for the isolation of whole spheroplaste and membrane preparations from the blue‐green alga Phormidium luridum which are active in photosystem‐II‐sensitized and photosystem‐I‐sensitized electron‐transport reactions and in photophosphorylation. Attention is called to the necessity of supplying magnesium and phosphate throughout the preparative and assay procedures for obtaining active membranes. Selective washing of a proper membrane preparation is shown to remove a new protein factor, termed protein factor 1, which restores the ability of the preparation to catalyze photosystem‐I‐sensitized reactions.