Regulation of skeletal muscle glycolysis during dehydration in the aestivating African clawed frog, Xenopus laevis
Seasonally arid conditions can trigger African clawed frogs (Xenopus laevis) to enter aestivation. This process includes whole body dehydration that at high levels can create hypoxic conditions due to impaired blood circulation and increase the need for glycolytic energy production. This thesis examines hexokinase (HK) and lactate dehydrogenase (LDH) purified from skeletal muscle of control versus dehydrated (~30% body water lost) frogs. Studies analyzed substrate affinities, urea effects, thermal stability and protein posttranslational modifications (PTM) to understand how enzyme properties are modified under dehydration stress. Muscle HK and LDH showed regulation by reversible protein phosphorylation and nitrosylation. These PTM’s correlated with reduced affinities for glucose by HK and lactate by LDH, overall lower Vmax for LDH in both directions, and altered thermal stabilities. The two enzymes responded to the same PTMs, which suggests that coordinated controls over these first and last enzymes of anaerobic glycolysis contribute to dehydration responsive pathway regulation.