Uptake of N-ethylmaleimide and I-Fluoro-2, 4-dinitrobenzene in relation to the irreversible inhibition of glucose transfer in the human erythrocyte.

1. The uptake of the inhibitors N-ethylmaleimide (NEM) and 1-fluoro-2,4-dinitrobenzene (DNFB) by human red cells has been correlated with the inhibition of glucose exit.2. With both inhibitors there was an initial rapid uptake by the cells with little inhibition; this was followed by a phase when inhibition was developing rapidly but uptake continued at a steady rate even after the development of inhibition had flattened off.3. The rate of uptake of DNFB during the rapid development of inhibition corresponded to about 4 x 10(8) molecules/cell for 100% inhibition, irrespective of the temperature of incubation. This cannot be used as an estimate of the number of glucose transfer sites in the cell membrane because of the lack of specificity.4. In an examination of lipids from red cells incubated with [(14)C]DNFB, labelling associated with lipids was eluted with peaks in chloroform-methanol 4:1 and 1:4 respectively. Thus, although DNFB is normally regarded as a protein reagent, involvement of lipids in the transfer of glucose could not be excluded.