Cytochrome c oxidase subunits in contact with phospholipids. Hydrophobic photolabeling with azidophospholipids.

The technique of photolabeling of membrane proteins with arylazidophospholipids was applied to cytochrome c oxidase. The "deep" and "shallow" labels employed reacted with all subunits of cytochrome c oxidase except V and VI: Subunits I, III, and VII were heavily labeled, Subunit II was labeled to a lesser extent, and Subunit IV was poorly labeled. Subunit I was labeled more by the deep label and Subunit VII by the shallow one. The other subunits were equally labeled by the two probes. This technique has revealed what subunits of cytochrome c oxidase interact with the lipid and their approximate position in the membrane.