IMPLICATIONS OF CONTROL-THEORY FOR HOMEOSTASIS AND PHOSPHORYLATION OF TRANSPORT MOLECULES

Homeostasis of a cytosolic substrate (e.g. H+) can be achieved by transmembrane transport. Control theory implies that the involved activation and deactivation of a transport molecule (as observed in patch clamp experiments) requires input of energy. This energy can be provided by a so‐called non‐consuming binding site or by other sources and is necessary in order to achieve asymmetric rate‐constants required for an efficient integral controller. Another important prediction of control theory is the involvement of two different binding sites for the substrate and its antagonist in order to define a non‐zero set‐point. The kinetic behavior of a homeostatic feed‐back loop is calculated. The system can generate weakly damped oscillations or exponential responses. Numerical calculations using data from the pH‐controller of Nitella show that a buffer is necessary in order to explain the observed long periods of 1 hour/cycle. Theoretically, the damping factor can originate from shunting transporters or from special terms of the biochemical reaction schemes. The effect of shunting transport systems is demonstrated in the case of data from the light‐effect on H+‐fluxes in Nitella. 1990 Deutsche Botanische Gesellschaft/German Botanical Society