A liposome-membrane low pH fusion method developed recently in our laboratory permits us to effect and monitor the in vitro incorporation of controlled quantities of natural as well as foreign lipids and proteins into purified functional biomembranes (Schneider, et al., PNAS, 77, 442, 1980). We have determined that the incorporation of foreign phospho-lipids into some cell membranes results in a remarkable increase in the average distances of various integral membrane proteins concomitant with both diminished activities and superactivities in various membrane functions. In our studies, we will use a purified functional preparation of the energy transducing membrane of the mammalian heart mitochondrion as a model membrane system which catalyzes a large number of diversified metabolic activities common to most cell membranes, and which conserves the metabolic energy essential to cell survival. Using our new fusion method, we will incorporate various quantities and combinations of phospholipids and cholesterol, as well as purified natural and foreign integral proteins into the membrane bilayer for the purpose of exploring the role of protein-protein and protein-lipid interactions in mechanisms basic to specific membrane functions such as ion and metabolite transport and exchange, oxidation-reduction activities, and the transduction of metabolic energy. The major objectives of our study are: (1) to determine the requirement of protein organization and immobility vs protein randomness and diffusion for normal and altered membrane activities; (2) to determine the requirement of lipid fluidity vs lipid stability for normal and altered membrane activities; and (3) to determine the effects of incorporation of natural and foreign integral proteins on membrane activities. We believe that our approach to these objectives represents a new and significant exploration in controlled structural and functional engineering of a biomembrane with possible consequences in the area of programmed, membrane model disfunctions, superfunctions, and new functions. Such in vitro engineering represents an exploration in the programming of models of membrane pathology.