EFFECTS OF DOMAIN-STRUCTURE ON INPLANE REACTIONS AND INTERACTIONS

The existence of an in-plane domain structure in biological membranes raises the question of the physiological function, if any, of this str ucture. One important function may be to enhance or limit the equilibr ium poise and rates of in-plane reactions through control by the cell of the percolation properties of the domain system. At low average dom ain occupancy by reactants or interactants, which must be the case for most biological membrane components, moving the domain system from co nnection to disconnection has marked effects on the apparent equilibri um poise and the rates of membrane-confined reactions. This conclusion is based on computer modelling of the effects of disconnection/connec tion of nine types of bimolecular in-plane reactions. Using the phase structure and percolation properties of two-component, two-phase phosp holipid bilayers, it is possible to examine experimentally homo- and h eterodimeriztion reactions, and enzyme-catalysed reactions in-plane as well as the effects of a transmembrane peptide on these systems. Thes e theoretical and experimental studies suggest that percolation effect s may be physiologically important in biological membranes. Whether th is is in fact the case remains to be demonstrated.