Binding of cytochalasin B to trypsin and thermolysin fragments of the human erythrocyte hexose transporter.

The cleavage of the human erythrocyte hexose transporter by the proteinases trypsin and thermolysin has been studied. When red cell membranes are treated with trypsin, washed and then photolabelled with cytochalasin B, a labelled peak at 18 kDa is obtained. This labelling of the cleaved transporter is D-glucose inhibitable. This probably indicates that the residual 36 kDa portion of the transporter is not required for binding of ligands. Extensive cleavage of the transporter with low concentrations of thermolysin only occurs when transporter is prelabelled with cytochalasin B. This indicates that covalently bound cytochalasin B can cause a conformational change which exposes the thermolysin cleavage site.