Characterization of the methylenediphosphonate transport system in Arthrobacter sp. GLP-1 using the novel tritium-labelled derivative.

The novel tritium-labelled derivative of methylenediphosphonate (MDP) was used in uptake studies of Arthrobacter sp. GLP-1 capable of utilizing a wide range of organophosphonates as its sole source of phosphorus. The MDP uptake was greatly stimulated upon phosphate deprivation. The uptake obeys Michaelis-Menten kinetics with respective Km and Vmax values of 33 microM and 0.3 nmol.min-1.mg-1 fr.wt. Glyphosate and pyrophosphate were competitive inhibitors of MDP uptake. The effect of orthophosphate was more complex than a mere inhibition of MDP uptake since activation occurred at low concentrations. The uptake of MDP by Arthrobacter sp. strain GLP-1 appears to be mediated by a transport system different from the glyphosate uptake system operating in the same cells. The driving force for MDP uptake by Arthrobacter sp. GLP-1 may be a proton gradient across the cell membrane.