Mono-, di- and tri-antennary d-galactose ligands as competitive inhibitors and photoaffinity labels of the hexose transporting system in erythrocytes. A model for the irreversible blocking of receptors in cell membranes

Starting from pentaerythritol, photolabile mono-, di-, and tri-dentate galactose derivatives as well as their 3H-labelled isotopomers were synthesised. The hydrophilic chains linking the 6 position of d-galactose to pentaerythritol consist of 13 atoms in line. The mono-, di- and tri-dentate compounds, although themselves not transported, inhibit in increasing order 14C-d-galactose transport into erythrocytes. On irradiating whole cells in the presence of ligand with 350-nm UV light, these compounds also in increasing order, could irreversibly block the hexose transport system. Irradiation without ligand has no effect. By using the 3H-labelled tridentate galactose compound the hexose transporter (zone 4.5) is specifically radiolabelled, as could be shown in an SDS-PAGE of membrane proteins from erythrocytes previously photoaffinity labelled. Radiolabelling is significantly supressed in the presence of d-glucose.