ATP-Dependent Active Transport Simulations Based on a Phosphatase–Channel–Kinase Membrane Structure K. FIATY, 1 C. CHARCOSSET, 1 B. PERRIN, 2 R. COUTURIER, 2 B. MAI ¨ STERRENA 2 1 Laboratoire d’Automatique et de Ge ´nie des Proce ´de ´s, UMR-CNRS 5007, CPE Lyon, Universite ´ Claude Bernard Lyon 1, Bat 308 G, 43 Bd du 11 novembre 1918, 69622 Villeurbanne cedex, France 2 Laboratoire Membranes Artificielles Biomime ´tiques, UMR-CNRS 5013, IUT A, Universite ´ Claude Bernard Lyon 1, Dpt de Ge ´nie Biologique, 43 Bd du 11 novembre 1918, 69622 Villeurbanne cedex, France Received 27 November 2003; Accepted 8 March 2004 DOI 10.1002/jcc.20051 Published online in Wiley InterScience (www.interscience.wiley.com). Abstract: Simulations of coupled interactions involving enzymatic reaction diffusion and electrostatic interactions were conducted under a fixed phosphatase– channel– kinase (PCK) topology oriented from the outside to the inside of a charged membrane structure. Depending on the phosphatase and kinase locations, we recently demonstrated that active transport of a phosphorylated substrate may occur via this PCK topology. The present analysis demonstrates that, if in addition to this topology, a phosphatase activity (P 1 ) is also present on the inner side of the membrane, but outside the unstirred layer surrounding the inner membrane surface, then active transport of the corresponding unphosphorylated substrate may also occur. Therefore, this PCK membrane topology, which behaves as a specific ATP-dependent transporter, appears as a general topology permitting; first, on its own the active transport of a phosphorylated substrate; second, when associated with a phosphatase acting in the bulk of the receiver compartment, the active transport of the corresponding unphosphorylated substrate, that is, in most cases, the transport of an uncharged substrate. The general mathematical model given permits the active transport of a phosphorylated substrate to be analyzed (in the absence of P 1 ), the active transport of an unphosphorylated substrate (in the presence of P 1 ), whatever the charge distributions on both sides of the membrane surface and whatever the positions of the membrane-bound phosphatase and the membrane-bound kinase. This general model also takes into account the consumption of ATP occurring into the receiver compartment during the time course of these transport phenomena. A broad analysis of the role played by the main parameters taken into account in the model was conducted to precisely define the physicochemical conditions and the membrane topology needed for the highest active transports within the shortest time. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 1264 –1276, 2004 Key words: ATP-dependent active transport simulations; phosphatase– channel– kinase structure Introduction Biomembranes are basically composed of lipid bilayers in which various proteins are systematically organized. These membrane proteins are believed to be responsible for a large variety of very efficient transport systems. 1 One of the goals of modern science is to mimic biomembrane behavior by creating artificial materials that can imitate natural biological structures and mechanisms. Starting from a simple mathematical model, 2 we have experi- mentally demonstrated that an alkaline phosphatase and a specific kinase acting on both parts of a charged porous membrane behave as an ATP-dependent transporter. 3,4 During the past few years, we have demonstrated that this topology (i.e., PCK topology) can lead to the active transport of small hydrophilic molecules, phosphor- ylated 5–7 or not, 8 following the properties reported for biological transport systems, that is, specificity and saturability. 2 It must be underlined that the proposed theoretical model exhibited good correlations with the experimental data. 2,8 Concomitantly, during this period, we have developed our previous mathematical model to a more general model, that is, closer to what can be expected in vivo. 9,10 Here we present the latest model that takes into account (1) the general kinetic rates of the enzymes involved in the system; (2) the relative positions of these enzymes (i.e., more or less far from the membrane surfaces); Correspondence to: B. Maı ¨sterrena; e-mail: maisterr@iuta.univ-lyon1.fr © 2004 Wiley Periodicals, Inc.