Phosphorylation of isocitrate dehydrogenase as a demonstration of enhanced sensitivity in covalent regulation

Abstract
The sensitivity to regulation of proteins undergoing covalent modification can be greatly increased when the substrates saturate the converter enzymes. This phenomenon, termed zero-order ultrasensitivity, occurs in the reversible phosphorylation of [Escherichia coli] isocitrate dehydrogenase. The possibility that this enhanced sensitivity is a common feature of covalent regulatory systems is discussed.