Phosphate distribution and transport in mycoplasma.

In Mycoplasma capricolum 75% of the total cell phosphate is found in the nucleic acids and polyphosphate fraction. The cold acid soluble fraction consisted primarily of orthophosphate (40 mM) in resting organisms. In metabolizing cells, phosphate esters, probably organophosphates, represented the largest part of that fraction (40 mM) whose content in orthophosphate is lowered to 10-15 mM. Phosphate is accumulated against its concentration gradient after its entry as orthophosphate. It is taken up by the cell by two different, energy-stimulated transport systems. The response of both systems to metabolizable substrates resembles what is described for other microorganisms. The high affinity system had a Km of 12.8 microM and the low affinity system had a Km of 1.1 mM when cells were grown in a phosphate-poor medium. Addition of phosphate (30 mM) to that medium modified both system kinetic properties. Inhibition of phosphate influx by arsenate is limited to the energy-stimulated portion of the influx in both systems.