Regulation of lactate dehydrogenase and glycerol-3-phosphate dehydrogenase in mammalian hibernation
Hibernation is a winter survival strategy for many small mammals. Animals sink into deep torpor, body temperature falls to near 0°C and physiological functions are strongly suppressed. Enzymes are the catalysts of metabolic pathways in cells and their appropriate control is critical to hibernation success. This thesis explores the properties and regulation of two key enzymes of carbohydrate metabolism (lactate dehydrogenase, LDH) and lipid metabolism (glycerol-3-phosphate dehydrogenase, G3PDH) purified from liver and skeletal muscle of ground squirrels (Urocitellus richardsonii). The studies showed that changes in pH, temperature, and inhibitors play roles in differentially regulating these enzymes between euthermic and torpid states. Furthermore, reversible protein phosphorylation proved to be a significant regulatory mechanism, producing a reduced activity state of skeletal muscle LDH and increased activity state of G3PDH in both skeletal muscle and liver during torpor. Overall, these studies showed that multiple mechanisms of enzyme regulation, particularly protein phosphorylation, contribute to reorganizing fuel metabolism during hibernation.