Bioenergetic characterization of transient state phosphate uptake by the cyanobacterium Anacystis nidulans. Theoretical and experimental basis for a sensory mechanism adapting to varying environmental phosphate levels

A force flow relationship based on nonequilibrium thermodynamics was derived to analyze the variable transient state phosphate uptake phenomena of cyanobacteria seen under different growth conditions and external phosphate concentrations. This relationship postulates the following basic properties of the uptake system: a threshold value exists, below which incorporation is energetically impossible. Threshold values are influenced by the activity of the phosphate uptake system, such that a decrease of the activity increases the threshold level. Near the thermodynamic equilibrium the uptake rate is linearly dependent on the free energy of polyphosphate formation and the pH-gradient at the thylakoid membrane. Experiments performed the Anacystis nidulans showed that phosphate uptake characteristics conformed to the properties predicted by the linear force-flow relationship.