Regulation of glutamate dehydrogenase and lactate dehydrogenase in the freeze tolerant wood frog, Rana sylvatica
Freeze tolerance is a survival strategy used by the wood frog, Rana sylvatica, for winter survival. Drastic changes to physiology and biochemistry are required to enter a state of metabolic rate depression in order to reestablish homeostasis during whole-body freezing. Enzymes are biocatalysts that mediate these metabolic functions and regulate survival of this environmental stress. This thesis explores the properties and regulation of two key enzymes of carbohydrate metabolism (lactate dehydrogenase, LDH) from liver and amino acid metabolism (glutamate dehydrogenase, GDH) from skeletal muscle. The studies showed that allosteric effectors play a role in differentially regulating these enzymes between freezing and control conditions. Furthermore, reversible protein phosphorylation appears to be a common regulatory mechanism reducing activity of both LDH and GDH in the frozen state. Altogether, these studies support theories that multiple mechanisms of enzyme regulation, particularly protein phosphorylation, contribute to the reorganization of metabolism during freeze tolerance.