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Magdeburg, Germany

The Max Planck Institute for Dynamics of Complex Technical Systems is located in Magdeburg, Germany. It was founded in 1996. It is one of 80 institutes in the Max Planck Society . Wikipedia.

Straube R.,Max Planck Institute for Dynamics of Complex Technical Systems
Science Signaling | Year: 2012

Jiang et al. (Research Article, 11 October 2011, DOI: 10.1126/scisignal. 2002152) used a combined experimental and computational modeling approach to study the dynamic response behavior of covalent modification cycles in the presence of downstream targets ("loads"). Despite remarkable agreement between experiments and model predictions, there exists an apparent discrepancy in their approach because the utilized theoretical model does not reflect the bifunctional nature of the enzyme system used in experiments. Furthermore, a simple extension of the model to the case of bifunctional enzymes yields predictions that are partially at variance with the experimental results. It seems that an appropriate mechanistic model would have to reconcile two apparent contradictory concepts: ultrasensitivity and bifunctionality.

Li S.,Max Planck Institute for Dynamics of Complex Technical Systems
Journal of chromatography. A | Year: 2010

A new improvement based on outlet fractionation and feedback has been developed for simulated moving bed (SMB) chromatography. In this contribution, this fractionation and feedback SMB (FF-SMB) concept is extended to the general scenario which integrates a simultaneous fractionation of both outlet streams. A model-based optimization approach, previously adopted to investigate single fractionation, is extended to consider this flexible fractionation policy. Quantitative optimization studies based on a specific separation problem reveal that the double fractionation is the most efficient operating scheme in terms of maximum feed throughput, while the two existing single fractionation modes discussed in our previous study are also significantly superior to the conventional SMB operation. The advantages of the double fractionation extension are further demonstrated in terms of several more detailed performance criteria. In order to evaluate the applicability of the fractionation and feedback modification, the effect of product purity, adsorption selectivity, column efficiency and column number on the relative potential of FF-SMB over SMB is examined. 2010 Elsevier B.V. All rights reserved.

Lorenz H.,Max Planck Institute for Dynamics of Complex Technical Systems | Seidel-Morgenstern A.,Otto Von Guericke University of Magdeburg
Angewandte Chemie - International Edition | Year: 2014

The provision of pure enantiomers is of increasing importance not only for the pharmaceutical industry but also for agrochemistry and biotechnology. In general, there are two rival approaches to provide pure enantiomers. The chiral approach is based on developing an asymmetric synthesis of just one of the enantiomers, while the racemic approach is based on separating mixtures of the two enantiomers. In the last few years remarkable progress has been achieved in the latter area. This Review focuses in particular on enantioselective crystallization processes and preparative chromatography, including hybrid processes and the incorporation of racemization steps. Several examples from our research are used for illustration purposes. © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Straube R.,Max Planck Institute for Dynamics of Complex Technical Systems
PLoS Computational Biology | Year: 2014

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. Previous studies have shown that systems with a bifunctional enzyme can adjust the phosphorylation level of the regulator protein independently of the total protein concentrations - a property known as concentration robustness. Here, I argue that two-component systems with a bifunctional enzyme may also exhibit ultrasensitivity if the input signal reciprocally affects multiple activities of the sensor kinase. To this end, I consider the case where an allosteric effector inhibits autophosphorylation and, concomitantly, activates the enzyme's phosphatase activity, as observed experimentally in the PhoQ/PhoP and NRII/NRI systems. A theoretical analysis reveals two operating regimes under steady state conditions depending on the effector affinity: If the affinity is low the system produces a graded response with respect to input signals and exhibits stimulus-dependent concentration robustness - consistent with previous experiments. In contrast, a high-affinity effector may generate ultrasensitivity by a similar mechanism as phosphorylation-dephosphorylation cycles with distinct converter enzymes. The occurrence of ultrasensitivity requires saturation of the sensor kinase's phosphatase activity, but is restricted to low effector concentrations, which suggests that this mode of operation might be employed for the detection and amplification of low abundant input signals. Interestingly, the same mechanism also applies to covalent modification cycles with a bifunctional converter enzyme, which suggests that reciprocal regulation, as a mechanism to generate ultrasensitivity, is not restricted to two-component systems, but may apply more generally to bifunctional enzyme systems. © 2014 Ronny Straube.

Straube R.,Max Planck Institute for Dynamics of Complex Technical Systems
Biophysical Journal | Year: 2013

Regulation by covalent modification is a common mechanism to transmit signals in biological systems. The modifying reactions are catalyzed either by two distinct converter enzymes or by a single bifunctional enzyme (which may employ either one or two catalytic sites for its opposing activities). The reason for this diversification is unclear, but contemporary theoretical models predict that systems with distinct converter enzymes can exhibit enhanced sensitivity to input signals whereas bifunctional enzymes with two catalytic sites are believed to generate robustness against variations in system's components. However, experiments indicate that bifunctional enzymes can also exhibit enhanced sensitivity due to the zero-order effect, raising the question whether both phenomena could be understood within a common mechanistic model. Here, I argue that this is, indeed, the case. Specifically, I show that bifunctional enzymes with two catalytic sites can exhibit both ultrasensitivity and concentration robustness, depending on the kinetic operating regime of the enzyme's opposing activities. The model predictions are discussed in the context of experimental observations of ultrasensitivity and concentration robustness in the uridylylation cycle of the PII protein, and in the phosphorylation cycle of the isocitrate dehydrogenase, respectively. © 2013 Biophysical Society.

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