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

Dawson, N. J. , Biggar, Y., Malik, A. I. and Storey, K. B. (2018) Increased transcript levels and kinetic function of pyruvate kinase during severe dehydration in aestivating African clawed frogs, Xenopus laevis. Comparative Biochemistry and Physiology - Part B: Biochemistry and Molecular Biology, 224, pp. 245-252. (doi: 10.1016/j.cbpb.2018.01.003) (PMID:29331521)

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Abstract

The African clawed frog, Xenopus laevis, can withstand extremely arid conditions through aestivation, resulting in dehydration and urea accumulation. Aestivating X. laevis reduce their metabolic rate, and rely on anaerobic glycolysis to meet reduced ATP demands. The present study investigated how severe dehydration affected the transcript levels, kinetic profile, and phosphorylation state of the key glycolytic enzyme pyruvate kinase (PK) in the liver and skeletal muscle of X. laevis. Compared to control frogs, severely dehydrated frogs showed an increase in the transcript abundance of both liver and muscle isoforms of PK. While the kinetics of muscle PK did not differ between dehydrated and control frogs, PK from the liver of dehydrated frogs had a lower Km for phosphoenolpyruvate (PEP) (38%), a lower Ka for fructose-1,6-bisphosphate (F1,6P2) (32%), and a greater activation of PK via F1,6P2 (1.56-fold). PK from dehydrated frogs also had a lower phosphorylation-state (25%) in comparison to the enzyme from control frogs in the liver. Experimental manipulation of the phosphorylation-state of liver PK taken from control frogs by endogenous protein phosphatases resulted in decreased phosphorylation, and a similar kinetic profile as seen in dehydrated frogs. The physiological consequence of dehydration-induced PK modification appears to adjust PK function to remain active during a metabolically depressed state. This study provides evidence for the maintenance of PK activity through elevated mRNA levels and a dephosphorylation event which activates frog liver PK in the dehydrated state in order to facilitate the production of ATP via anaerobic glycolysis.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Dawson, Dr Neal
Authors: Dawson, N. J., Biggar, Y., Malik, A. I., and Storey, K. B.
College/School:College of Medical Veterinary and Life Sciences > Institute of Biodiversity Animal Health and Comparative Medicine
College of Medical Veterinary and Life Sciences > School of Biodiversity, One Health & Veterinary Medicine
Journal Name:Comparative Biochemistry and Physiology - Part B: Biochemistry and Molecular Biology
Publisher:Elsevier
ISSN:1096-4959
ISSN (Online):1879-1107
Published Online:10 January 2018

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