Increased transcript levels and kinetic function of pyruvate kinase during severe dehydration in aestivating African clawed frogs, Xenopus laevis

­Characterization of pyruvate kinase from the anoxia tolerant turtle, Trachemys scripta elegans: a potential role for enzyme methylation during metabolic rate depression

“…A reduction in PK activity during periods of anoxia has been well documented in literature. Notably, the dehydration tolerant frog Xenopus laevis has been shown to increase the affinity of PK for PEP when the enzyme is dephosphorylated, much like in the turtle ( Dawson et al, In press ). Furthermore, a change in PK activity was measured in adult mangrove snail ( Littorina scabra angulifera ) foot muscle in response to anoxia ( Fields & Ellington, 1992 ).…”

Reversible Enzyme Phosphorylation as a Mechanism for Metabolic Adaptation to Dehydration in the Skeletal Muscle of the African Clawed Frog, Xenopus laevis

“…Previous work on the effects of whole-body dehydration on X. laevis have provided preliminary evidence to describe the role that reversible protein phosphorylation has in the molecular response to this stress. It has been shown that reversible protein phosphorylation affects a broad range of processes including transcription factor binding and enzyme kinetic properties in X. laevis Dawson et al, 2018;Katzenback et al, 2014;Storey, 2011, 2009). However, reversible protein phosphorylation are known to be ubiquitous and the results of these modifications are often tissue-specific (Olsen et al 2006;Humphrey et al 2015).…”

“…The fact that glycolysis is critical for survival during dehydration is corroborated by the lactate concentrations that increase dramatically as soon as dehydration reaches a point where oxygen delivery is compromised (Hillman 1978b). Indeed, transcript levels and activities of PK are also maintained likely to ensure that PK activities stay high in dehydrating tissue to sustain the glycolytic pathway and supply pyruvate to LDH (Dawson et al 2018). Indeed, a study on locomotion during dehydration in these frogs indicates that the loss of water causes a decline in skeletal muscle ability to synthesize ATP by aerobic means, which further signals that dehydrated X. laevis has an increased dependence on glycolysis for energy production (Gatten 1987).…”

“…A restriction of oxygen availability necessitates a greater reliance on glycolysis for ATP production and the presence of modified regulatory mechanisms to fine tune glycolysis to energy needs. Certainly, glycolysis in X. laevis has been demonstrated to be strictly regulated through protein phosphorylation of key enzymes under high levels of dehydration exposure Storey 2016, 2019;Dawson et al 2018). These studies have documented significant changes in both enzyme maximal velocities and substrate affinities upon whole animal dehydration that appear to maintain forward flux through the pathway.…”

“…).At the other end of glycolysis, a characterization of skeletal muscle pyruvate kinase (PK) and lactate dehydrogenase (LDH) provides evidence of a shift towards continued anaerobic glycolysis during dehydration. Although there were no changes in PK kinetic parameters, transcript levels of PK increased in X. laevis skeletal muscle during HK: hexokinase (Childers and Storey 2016), LDH: lactate dehydrogenase (Childers and Storey 2019), PK: pyruvate kinase(Dawson et al 2018), GDH: glutamate dehydrogenase (Appendix 1). Green arrows are the predicted directions of metabolic flux determined from previous experiments.…”