Multimodulation of Phosphofructokinases in Metabolic Regulation

Enzyme physiology has proceeded within less than three decades from mere catalysis (no matter how efficient) to specific regulatory mechanisms, and to multimodulation of enzyme activity. Multimodulation makes possible the integration of a variety of signals by certain enzymes (Sols 1979, 1981). The importance of multimodulation has been obscured by uncritical claims piling up and reaching in some cases a bewildering multiplicity. For proper understanding of metabolic regulation it is necessary to sort out facts from artefacts, and biologically relevant mechanisms from in vitro curiosities. An outstanding case in this respect is phosphofructokinase, certainly a key enzyme in metabolic regulation (Sols 1976) and one long subjected to inflationary pressure with respect to mechanisms for the regulation of its activity, particularly in higher animals. The recent finding of metabolic interconversion of this enzyme in certain animal tissues makes a detailed discussion of the multimodulation of phosphofructokinase of particular interest in the context of this Symposium.