Inhibition of glucose transport by phenylglyoxal: Both dissipation of ΔpH and essential arginyl residues are involved

The effects of the arginine modifying reagent phenylglyoxal (PGO) on solute transport was studied in two cellular systems: protoplasts isolated from the mesophyll of Vicia faba L. and XD cell suspension culture of Nicotiana tabacum L. cv. Xanthi. The solutes in the case of the protoplasts were the non-metabolizable glucose analog 3-O-methyl-D-glucose (MeG), and a non-metabolizable amino acid analog α-aminoisobutyric acid (AIB), whereas the solutes for the cell suspension were AIB and nitrate. Solute transport in both systems was rapidly inhibited by PGO. Exposure of the protoplasts to light enhanced the initial rate of MeG uptake. PGO rapidly inhibited MeG uptake in both the light and the dark, the half-time for inactivation being less than 3 min. Flux analysis of double-labeled MeG showed that initial MeG uptake was mediated mainly by the plasma membrane transport system and that it was inhibited by PGO. Maximal inhibition of initial MeG uptake rate was observed at PGO concentrations of 1 mM and above. PGO treatment altered rapidly the equilibrium distribution of the ΔpH probe dimethyloxazolidine (DMO) in both cellular systems, indicating dissipation of ΔpH between cell and medium. In the protoplasts, PGO inhibited both DMO and MeG uptake at pH 5.5; however, at pH 7.0, where ΔpH is minimal, only MeG uptake was inhibited. Our results suggest that PGO has two effects on glucose uptake: an indirect effect through ΔpH dissipation and a direct effect through interaction with essential arginyl residues in the glucose transporter.