Labelling of egg phosphatidylcholine vesicles and myelin membrane with a photoreactive lipophilic reagent

The preparation and isolation of [3H]phenyl azide, a photosensitive non-polar probe, is reported. The reagent partitions into the lipid bilayer of egg phosphatidylcholine vesicles and bovine myelin membranes. On photoactivation to generate the nitrene grouping, as much as 90% of the covalently attached label is associated with the fatty acyl residues of the constituent phospholipid molecules. The remainder is found in the polar head groups. The cholesterol component of myelin membranes is also heavily labelled. These results suggest that such reagents may be used to probe the hydrophobic regions of natural membranes.