Alterations in the electron transfer chain in mutant strains of Escherichia coli lacking phosphatidylethanolamine

Inside-out sealed membrane vesicles were prepared from strains of Escherichia coli engineered to be lacking in the major phospholipid of this organism, phosphatidylethanolamine (DeChavigny, A., Heacock, P. N., and Dowhan, W. (1991) J. Biol. Chem. 266, 5323-5332). The energy transducing properties, namely the ability to generate a proton gradient directed inward and to transport electrons to molecular oxygen, were compared to those of membranes isolated from wild type cells containing normal levels of phosphatidylethanolamine. Membranes from both cell types were equal in their ability to oxidize succinate and lactate as well as hydrolyze ATP with the generation of proton gradients of similar magnitude, thus establishing the structural integrity of the membrane barrier and basic functionality of the energy transducing systems in the mutant membranes. However, mutant membranes were reduced by about 80% in their type II NADH dehydrogenase-dependent oxidase activity which resulted in a reduced ability to generate a proton gradient using NADH as an energy source. Use of artificial electron acceptors indicated that the level of type II NADH dehydrogenase activity was normal. Whole chain NADH oxidase activity could be restored by addition of short chain analogs of the naturally occurring Q8, even though the level of the Q8 pool in both cell types was the same. These results suggest that the function of Q8 in linking type II NADH dehydrogenase with the terminal oxidase(s) is dependent on the phosphatidylethanolamine content of the surrounding phospholipid matrix.