Interaction of succinate--ubiquinone reductase (complex II) with (arylazido)phospholipids

The interaction of purified succinate dehydrogenase and succinate--ubiquinone reductase (complex II) with lipids was explored by using two (arylazido)phospholipids, one with the reactive nitrene in the head-group region of the bilayer [1-palmitoyl-2-(2-azido-4-nitrobenzoyl)-sn-glycero-3-[3H]phosphocholine (PLII)] and one with the nitrene on the methyl terminus of one of the fatty acid chains [1-myristoyl-2-[12-[(2-azido-4-nitrophenyl)amino]lauroyl]-sn-glycero-3-[14C]phosphocholine (PLI)]. Protein was reacted with vesicles of egg lecithin containing radioactive (arylazido)-phospholipids and the covalent cross-linking of lipid and protein induced by irradiation under UV light. Purified succinate dehydrogenase was found to bind to lipid vesicles through both subunits as both were labeled by PLII. The smaller subunit was inserted into the interior of the bilayer and labeled by PLI. Complex II was found to interact with lipid vesicles, with the smaller subunit of succinate dehydrogenase, CII-3, and CII-4 all inserted into the interior of the bilayer. The large subunit of succinate dehydrogenase was found to be held above the bilayer in complex II and not labeled by either probe. Results are used to derive a picture of the arrangement of subunits in complex II and to evaluate the utility of (arylazido)-phospholipids in membrane studies.