DYNAMIC ASPECTS OF CASCADE-TYPE METABOLIC REGULATION

Cascade-type regulation, where certain enzymes in response to physiological signals modify the activity of other enzymes by covalent modification, is found in many organisms. We study the covalent regulation of glutamine synthetase which is involved in ammonia fixation in the bacterium Escherichia coli. In this paper we pose the question whether this type of regulation of glutamine synthetase has, under certain growth conditions an advantage over other types of regulation, e.g., allosteric regulation. We propose that the relatively slow dynamics of cascade-type regulation has an evolutionary advantage under conditions of fluctuating ammonia concentrations.