Reversible Enzyme Phosphorylation as a Mechanism for Metabolic Adaptation to Dehydration in the Skeletal Muscle of the African Clawed Frog, Xenopus laevis
Bibliographic record
Abstract
Xenopus laevis, although mainly an aquatic frog, lives in seasonally arid regions of southern Africa where well-developed dehydration tolerance is needed when ponds dry up.Frogs can endure about 40% loss of total body water leading to increased hematocrit and blood viscosity that restrict blood and oxygen delivery to tissues, elevate tissue osmolality, and lead to accumulation of lactate and urea.As one response to dehydration, frogs show restricted blood flow to skeletal muscle to preferentially maintain supply to the brain and internal organs.I hypothesized that dehydration stress triggers modifications to cellular energy production in skeletal muscle and could recruit alternative fuel use.This thesis explores metabolic regulation of enzymes (aldolase, CK, IDH), and energy stress signaling (via AMPK) in skeletal muscle of X. laevis.A particular focus was put on regulation via protein posttranslational phosphorylation to adapt enzyme activity and substrate affinity to changing physiological needs during dehydration.Analysis of kinetic parameters found that aldolase, CK and IDH all showed reduced maximal velocities and altered substrate affinities during dehydration.Downregulation of aldolase suggested a reduction in glycolytic rate during dehydration, moderating the use of glucose, whereas CK regulation modulates phosphocreatine consumption.Substrate affinities of both CK and IDH were dependent on magnesium concentrations.CK was more active at higher Mg 2+ concentrations that occur as tissues dehydrate whereas IDH showed increased affinity for Mg 2+ that could shift the reaction to favor α-KG production during dehydration.I hypothesized that changes to muscle energetics would stimulate the action of AMPK and its downstream effectors to promote a fuel switching from carbohydrates to include fats during dehydration.However, iv phosphorylated AMPK (activated) did not increase and the regulation of two key downstream AMPK targets, acetyl-coA carboxylase and Unc-51 like autophagy activating kinase 1, did not indicate recruitment of fatty acid metabolism or autophagy for energy during dehydration in skeletal muscle.Overall, these studies showed that reversible protein phosphorylation has a prominent role in controlling X. laevis skeletal muscle enzyme function and reorganization of metabolic pathways during whole animal dehydration.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".