Operating regimes of covalent modification cycles at high enzyme concentrations

JOURNAL OF THEORETICAL BIOLOGY

卷:431

Article

Straube, Ronny^1,2 

[1] Friedrich Alexander Univ Erlangen Nuernberg, Dept Math, Cauerstr 11, D-91058 Erlangen, Germany

[2] Max Planck Inst Dynam Complex Tech Syst, Sandtorstr 1, D-39106 Magdeburg, Germany

关键词: Total quasi-steady state approximation;    Stimulus-response curve;    Concentration robustness;   

DOI  :  10.1016/j.jtbi.2017.08.006

来源: Elsevier

【 摘 要 】

The Goldbeter-Koshland model has been a paradigm for ultrasensitivity in biological networks for more than 30 years. Despite its simplicity the validity of this model is restricted to conditions when the substrate is in excess over the converter enzymes - a condition that is easy to satisfy in vitro, but which is rarely satisfied in vivo. Here, we analyze the Goldbeter-Koshland model by means of the total quasi-steady state approximation which yields a comprehensive classification of the steady state operating regimes under conditions when the enzyme concentrations are comparable to or larger than that of the substrate. Where possible we derive simple expressions characterizing the input-output behavior of the system. Our analysis suggests that enhanced sensitivity occurs if the concentration of at least one of the converter enzymes is smaller (but not necessarily much smaller) than that of the substrate and if that enzyme is saturated. Conversely, if both enzymes are saturated and at least one of the enzyme concentrations exceeds that of the substrate the system exhibits concentration robustness with respect to changes in that enzyme concentration. Also, depending on the enzyme's saturation degrees and the ratio between their maximal reaction rates the total fraction of phosphorylated substrate may increase, decrease or change nonmonotonically as a function of the total substrate concentration. The latter finding may aid the interpretation of experiments involving genetic perturbations of enzyme and substrate abundances. (C) 2017 Elsevier Ltd. All rights reserved.

【 授权许可】

Free