MAGNESIUM ADENOSINE 5'-TRIPHOSPHATE-ENERGIZED TRANSPORT OF GLUTATHIONE-S-CONJUGATES BY PLANT VACUOLAR MEMBRANE-VESICLES

By characterization of the uptake of glutathione-S-conjugates, princip ally dinitrophenyl-S-glutathione (DNP-GS), by vacuolar membrane vesicl es, we demonstrate that a subset of energy-dependent transport process es in plants are not H+-coupled but instead are directly energized by MgATP. The most salient features of this transport pathway are: (a) it s specific, obligate requirement for MgATP as energy source; (b) the n ecessity for hydrolysis of the gamma-phosphate of MgATP for uptake; (c ) the insensitivity of uptake to uncouplers of the transtonoplast H+ g radient (carbonylcyanide 4-trifluoromethoxyphenylhydrazone, gramicidin -D), and NH4Cl); (d) its pronounced sensitivity to vanadate and partia l inhibition by vinblastine and verapamil; (e) the lack of chemical mo dification of DNP-GS either during or after transport; (f) the capacit y of S-conjugates of chloroacetanilide herbicides, such as metolachlor -GS, but not free herbicide, to inhibit uptake; and (g) the ability of vacuolar membrane vesicles purified from a broad range of plant speci es, including Arabidopsis, Beta, Vigna, and Zea, to mediate MgATP-depe ndent, H+-electrochemical potential difference-independent DNP-GS upta ke. On the basis of these findings it is proposed that the transport o f DNP-GS across the vacuolar membrane of plant cells is catalyzed by a glutathione-conjugate transporter that directly employs MgATP rather than the energy contained in the transtonoplast H+-electrochemical pot ential difference to drive uptake. The broad distribution of the vacuo lar DNP-GS transporter and its inhibition by metolachlor-GS are consis tent with the notion that it plays a general role in the vacuolar sequ estration of glutathione-conjugable cytotoxic agents.