Publisher Summary This chapter discusses the role of futile cycles in thermogenesis and metabolic control. Cyclic processes are common in metabolism. They serve many functions, in oxidation and synthesis, in the generation of energy and reducing equivalents, and in transfer and transport of a variety of compounds and reducing equivalents against energy barriers or through membranes. However, there is one type of cycling whose function is not immediately apparent. These cycles may occur when there are two opposing metabolic pathways in the cell in which the reactions in the forward and reverse directions are catalyzed by separate enzymes. Cellular metabolism is thought of as tightly regulated, so that the operation of “useless” energy-dissipating reactions has been commonly discounted. Liver parenchymal cells and kidney cortex cells contain the complete complement of enzymes for the synthesis of glucose and glycogen and also for glycolysis. Many of the reactions are readily reversible and are common to both pathways, but the key steps are unique to each path and irreversible because of the energy barriers.

Futile Cycles in the Metabolism of Glucose

Role of calcium in the hormonal regulation of liver metabolism

Studies on the inhibition of hepatic lipogenesis by N6,O2′-dibutyryl adenosine 3′,5′-monophosphate☆

Hepatic pyruvate kinase. Regulation by glucagon, cyclic adenosine 3'-5'-monophosphate, and insulin in the perfused rat liver.

The role of calcium ion as a mediator of the effects of angiotensin II, catecholamines, and vasopressin on the phosphorylation and activity of enzymes in isolated hepatocytes.

Rapid reciprocal changes in rat hepatic glycolytic enzyme and fructose diphosphatase activities following insulin and glucagon injection.

Ethanol-Induced Inhibition of Human Intestinal Enzyme Activities: Reversal by Folic Acid

Rapid Reciprocal Changes in Rat Tissue Enzyme Activities following Epinephrine Injection

Fructose-1,6-diphosphatase deficiency, hypoglycemia, and response to folate therapy in a mother and her daughter.

Hormonal regulation of hepatic and jejunal formiminotransferase activity in man and rat.

Fred B. Stifel

Papers

Rapid reciprocal changes in rat hepatic glycolytic enzyme and fructose diphosphatase activities following insulin and glucagon injection.

Ethanol-Induced Inhibition of Human Intestinal Enzyme Activities: Reversal by Folic Acid

Rapid Reciprocal Changes in Rat Tissue Enzyme Activities following Epinephrine Injection

Fructose-1,6-diphosphatase deficiency, hypoglycemia, and response to folate therapy in a mother and her daughter.

Hormonal regulation of hepatic and jejunal formiminotransferase activity in man and rat.