Berlin 2008 – wissenschaftliches Programm

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BP: Fachverband Biologische Physik

BP 17: Physics of Cells

BP 17.7: Vortrag

Mittwoch, 27. Februar 2008, 15:30–15:45, PC 203

Transmembrane Potential and Proton Buffering Capacity of a Small Vesicle — •Tihamér Geyer and Sarah Blaß — Zentrum für Bioinformatik, Universität des Saarlandes, D 66041–Saarbrücken

The dynamic behavior of a metabolic network is determined both by the reaction rates and by the buffering capacities of the reservoirs. While a lot of effort goes into determining rate constants, much less emphasis is put on the capacities. Consequently, for setting up a dynamic simulation of a part of the metabolism of a cell, it is much easier to gather the necessary rates than to find reliable information on how to describe, e.g., a proton buffering capacity in a typical in vivo geometry like a small vesicle.

To shed some more light onto how to incorporate a specific biological setup into a simulation, we used stochastic molecular simulations of a photosynthetic vesicle of the purple bacterium Rhodobacter sphaeroides to investigate how the transmembrane potential ΔΦ has to be described in order to reproduce the measured time course after a short flash of light. By treating the small vesicle as a spherical capacitor, both the biphasic rise and the exponential decay of ΔΦ are reproduced, while a Nernst-like model based on the pH gradient leads to a different signature in time. The simulation also reproduces the simultaneously measured cytochrome c oxidation state.

We also discuss how the findings from the vesicle apply to other confined geometries as, e.g., the cristae of the mitochondria.