Passive membrane permeation of small molecules

Membrane permeability of small molecules, the main focus of this thesis, is a key topic in scientific research and in areas of biotechnology, pharmacy and biomedicine. In Chapter I, I introduce the basic features of biological membranes and the current state-of-art about lipids, lipid phases and the role of lipid composition on membrane permeability. In chapter II, I present a (stopped-flow) fluorescence-based approach to estimate the permeability of water and weak acids in lipid vesicles (in vitro) and through the plasma membrane of living cells, specifically Saccharomyces cerevisiae (in vivo). This led to the writing of a user-friendly protocol, presented in Chapter III, to perform the permeability measurements and analysis in a standardized manner. In Chapter IV, I present the permeability of a variety of small molecules through synthetic membranes of different lipid composition. In particular, we combined our stopped-flow kinetic measurements with molecular dynamics simulations in order to acquire detailed molecular insight into the mechanism of solute permeation. Chapter V is an extract of a bigger work entitled The structure and function of the bacterial osmotically-inducible protein Y. Here, I focus on the permeability of membranes for water and the role of aquaporin Z (AqpZ).