9404702 Tollin The principal question being asked in this project is the following: how do the properties of lipid bilayers modulate the protein-protein interaction and electron transfer processes which occur between integral and peripheral membrane redox proteins during their functioning as components of the respiratory and photosynthetic energy transduction systems? Experiments addressing this question will utilize reconstituted proteolipid systems in which the lipid and protein compositions can be readily varied. The lipid bilayer properties to be investigated are: i. fatty acid composition, which determines the fluidity of the membrane interior; ii. head group identity, which modulates electrical charge, hydration, curvature free energy, lateral mobility and other surface physicochemical properties; iii. presence of specific components such as cardiolipin and glycolipids. The protein systems to be studied include the integral membrane proteins cytochrome c oxidase (bovine heart) and cytochrome f (spinach), and their physiological electron transfer partners, the peripheral membrane proteins cytochrome c (bovine heart) and plastocyanin (spinach). Our approach is multifaceted, utilizing a unique combination of kinetic, thermodynamic and structural techniques. Protein-protein complex formation and electron transfer will be characterized by measurements of transient kinetics using laser flash photolysis and by electrochemistry at lipid bilayer-modified electrodes; structural features of the proteolipid systems (packing density and film thickness) and protein-protein and protein-lipid interactions will be investigated using surface plasmon resonance spectroscopy. %%% *** In this research program, we wish to determine how the lipid components of biological membranes modulate the properties of the proteins which participate in the principal energy conversion processes occurring in biology, i.e. photosynthesis in green plants (which converts sunlight into f ood energy in the form of carbohydrate) and respiration in animals (which converts stored carbohydrate into biologically available energy). We will change the following properties of the lipid component and determine how these changes affect protein-protein interactions and electron transfer reactions: fatty acid composition (which modulates membrane fluidity), lipid head group structure (which modulates surface electrical charge), and the presence or absence of specific types of lipids (galactolipids and cardiolipin) which are unique components of the biological membranes associated with photosynthesis and respiration. The following properties of the protein-lipid systems will be studied: the rates of protein-protein electron transfer reactions, the intrinsic ability of proteins to accept and donate electrons, and the structural changes induced in the lipid-protein systems by varying the lipid properties noted above. These studies will not only be of fundamental interest for increasing our understanding of these crucially important biological processes, but will also have important implication for the development of future technologies such as molecular electronic devices, biosensors for medical diagnosis, and energy conversion devices based upon biological models. ***
