Selective labeling of the hydrophobic core of membranes with 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine, a carbene-generating reagent

The synthesis of a new photoactivatable probe, 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine ([125I]-TID), with a high specific radioactivity (10 Ci mmol-1) is described. It was tested as a probe for the hydrophobic core of membranes. TID partitions strongly in favor of the lipid phase of membranes, and the photogenerated carbene labels intrinsic membrane proteins in a highly selective manner. This conclusion was reached from the distribution of radioactivity among the proteins of [125I]TID-labeled human erythrocyte membranes. By far the most heavily labeled protein is band 3 [nomenclature of Fairbanks, G., Steck, T. L., & Wallach, F. G. H. (1971) Biochemistry 10, 2606-2617] while the labeling of glycophorin is approximately 5 times less than that of band 3. There is little or no labeling of known extrinsic proteins.