Phospholipids Containing Photoactivable Groups in Studies of Biological Membranes *

Photoactivable carbene precursors, aryl diazirines and trifluorodiazopropionates, were incorporated synthetically into the omega-positions of fatty acids, which were used to synthesize phospholipids. Extensive intermolecular C--H insertion reactions were demonstrated by photolysis of liposomes prepared from the above phospholipids. Structural analysis of the cross-linked products showed that the predominant sites of cross-linking were in the expected positions within the bilayer. Studies on the topography of a number of membrane proteins using the above phospholipids were initiated. Cross-linking of the photoactivable phospholipids to membrane-embedded proteins, glycophorin A, cytochrome b5, and gramicidin A, was demonstrated.