Assembly of lipids and proteins in escherichia coli membranes

Presently there is much interest in the relationship between the structure and function of biological membranes. An approach to the understanding of this relationship has been the study of the effect of the modification of the membrane lipids on the function of membrane‐associated activities. In our laboratories we have modified the apolar portion of the membrane lipids of unsaturated fatty‐acid auxotrophs of Escherichia coli and investigated the effect of such modifications on enzymes of the electron‐transport system. From these studies we were able to conclude that E. coli regulates the relative fatty‐acid content of its phospholipids and maintains a certain membrane fluidity necessary for proper membrane function (1–3). We have also proposed that lipids are heterogeneously distributed within the membrane in domains of differing fluidity (4). The studies of McConnell, Chapman, and others (5–13) have corroborated these concepts and extended them to other biological and model membranes. In this paper we review some of our previous results and present evidence to show how NADH and D‐lactate oxidases of E. coli membranes are influenced by the fluid states of membrane phospholipids. Preliminary evidence is also presented to show that biogenesis of membranes probably occurs by independent insertion into the membranes of lipids and proteins which upon subsequent interaction with each other form the functional lipoprotein units.