The regulation of the energy-dependent phosphate uptake by the blue-green alga Anacystis nidulans.

Investigations of the energy-dependent accumulation of orthophosphate by the blue-green alga Anacystis nidulans have established: 1. The transport through the cell membrane is the rate-limiting step in the incorporation of phosphate.-2. This transport is facilitated by a "carrier" that can be activated by Ca(2+) and Mg(2+) and inhibited by EDTA.-3. The activation of the carrier in the light is associated with changes of the cytoplasmic Mg(2+) content.-4. Intracellular phosphate is shown to be present in bound form.-5. The energy-dependent accumulation of orthophosphate within the cell depends strictly on the cytoplasmic pH and not on the energy conversion at the thylakoid membrane which is responsible for the energy supply. The cytoplasmic pH is different in the light, in the dark, and in the presence of the uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP). Orthophosphate accumulation can most readily be explained in terms of a pH dependent precipitation into a complex with bivalent cations rather than by an active transport against a concentration gradient.