How does homeostasis emerge from the activities of many individual enzymes?

Metabolic homeostasis maintains appropriate levels of energy and biosynthetic precursors under variable conditions. To achieve this, metabolic pathways are regulated by a combination of mass action and allosteric feedback. We have extensive knowledge of the molecular details of the allosteric regulation of many individual enzymes, but our understanding of how metabolic homeostasis emerges from the activities of individual enzymes is incomplete, and the number of allosteric regulators that remain to be discovered is unknown. Here, I will describe our recent work using a combination of biophysical modeling and experiments to identify the function of several conserved allosteric regulators of the glycolysis pathway. Specifically, we discovered that the function of allosteric regulation of hexokinase and phosphofructokinase by ATP, ADP, inorganic phosphate, and glucose-6-phosphate is to maintain high ATP levels and to prevent uncontrolled accumulation of phosphorylated intermediates of glycolysis by inhibiting the reaction of Harden and Young. Our methodology can be applied to any other metabolic pathway and provides a framework for understanding how individual enzymes work together to maintain cellular metabolic homeostasis.