Ronny Straube

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A common scenario in cellular signal transduction is that a diffusing surface-bound molecule must arrive at a localized signaling region on the cell membrane before the signaling cascade can be completed. In order to determine the timescale for this process, we calculate asymptotic results for the mean first passage time for a diffusing particle confined to(More)
The mean first passage time (MFPT) is calculated for a Brownian particle in a spherical domain in R 3 that contains N small non-overlapping absorbing windows, or traps, on its boundary. For the unit sphere, the method of matched asymptotic expansions is used to derive an explicit three-term asymptotic expansion for the MFPT for the case of N small locally(More)
Purple non-sulfur bacteria (Rhodospirillaceae) have been extensively employed for studying principles of photosynthetic and respiratory electron transport phosphorylation and for investigating the regulation of gene expression in response to redox signals. Here, we use mathematical modeling to evaluate the steady-state behavior of the electron transport(More)
Biomembranes consist of a lipid bi-layer into which proteins are embedded to fulfill numerous tasks in localized regions of the membrane. Often, the proteins have to reach these regions by simple diffusion. Motivated by the observation that IP 3 receptor channels (IP 3 R) form clusters on the surface of the endoplasmic reticulum (ER) during ATP-induced(More)
Two-component signal transduction systems, where the phosphorylation state of a regulator protein is modulated by a sensor kinase, are common in bacteria and other microbes. In many of these systems, the sensor kinase is bifunctional catalyzing both, the phosphorylation and the dephosphorylation of the regulator protein in response to input signals.(More)
We asymptotically calculate the spatially averaged mean first passage time (MFPT) of a diffusing channel protein in a finite membrane patch containing a small absorbing anchor site. Different two-dimensional membrane geometries are considered including a circular, a square-shaped, a rectangular, and a cylindrical domain. The asymptotic expressions are found(More)
The dynamics of glycolytic waves in a yeast extract have been investigated in an open spatial reactor. At low protein contents in the extract, we find a transition from inwardly moving target patterns at the beginning of the experiment to outwardly moving spiral- or circular-shaped waves at later stages. These two phases are separated by a transition phase(More)
Calcium ions (Ca(2+)) are an important second messenger in eucaryotic cells. They are involved in numerous physiological processes which are triggered by calcium signals in the form of local release events, temporal oscillations, or reaction-diffusion waves. The diffusive spread of calcium signals in the cytosol is strongly affected by calcium-binding(More)
Intracellular signaling gradients naturally arise through a local activation of a dif-fusible signaling molecule, e.g. by a localized kinase, and a subsequent deactivation at a distant cellular site, e.g. by a cytosolic phosphatase. Here, we consider a spherical cell containing a finite number of small spherical compartments where a signaling molecule(More)
In the simplest case, substrate competition arises if two ligands compete for access to a single binding site of a receptor protein (or enzyme). If the two ligands exhibit different binding affinities the competition becomes biased: as long as the receptor concentration remains lower than that of the high-affinity ligand the latter blocks all of the(More)