Reconstitution of cyanobacterial photophosphorylation by a latent Ca2+-ATPase.

Photosynthetic membranes derived from sonic extracts of the cyanobacterium $\text{Spirulina}\text{platensis}$ contain a latent Ca⁺²-ATPase which is activated by exposure to trypsin. When sonic membranes are washed with ethylenediaminetetraacetic acid, the ATPase is removed from these membranes with an accompanying loss of photophosphorylation activity. The latent ATPase activity solubilized by washing has been partially purified, and addition of the enzyme to depleted membranes restores photophosphorylation activity to levels approaching 50% of the rates observed in unwashed membranes. These data indicate that this ATPase is the coupling factor responsible for photosynthetic energy transduction in $\text{Spirulina}\text{platensis}$.