Phosphate transport in Ehrlich ascites tumor cells and the effect of arsenate

The effect of extracellular Pi and arsenate on Pi-transport in Ehrlich ascites tumor cells has been studied. Pi-transport can be described by Michaelis-Menten kinetics; the maximal flux equal to 44 mmoles (kg cell water)^?1 hour^?1 and K_m equal to 3.3 × 10^?4 M . Arsenate is a competitive inhibitor of Pi-transport with an inhibition constant (K_i) equal to 2.41 × 10^?3 M . The data support the hypothesis that cellular Pi is regulated by the cell membrane through the mediation of a carrier system.