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Corpus Systématique Animale

Titre du document

Urea and salt effects on enzymes from estivating and non-estivating amphibians

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Springer (journals)
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Mots-clés d'auteur
  • Scaphiopus couchii
  • Rana pipiens
  • estivation
  • pyruvate kinase
  • phosphofructokinase
  • urea effects on enzymes
  • metabolic arrest
  • PFK : 6-phosphofructo-1-kinase
  • PK : pyruvate kinase
Nom du fichier dans la ressource
Batraciens_v2b_00519, Poissons_v2b_005016
  • Jean E. Grundy 1
  • Kenneth B. Storey 1
  • 1) Institute of Biochemistry and Department of Chemistry, Carleton University, K1S 5B6, Ottawa, Ontario, Canada

The effects of urea, cations (K+, NH4, Na+, Cs+, Li+), and trimethylamines on the maximal activities and kinetic properties of pyruvate kinase (PK) and phosphofructokinase (PFK) from skeletal muscle, were analyzed in two anuran amphibians, an estivating species, the spadefoot toadScaphiopus couchii, and a semi-aquatic species, the leopard frogRana pipiens. Urea, which accumulates naturally to levels of 200–300 mM during estivation in toads, had only minor effects on the Vmax, kinetic constants and pH curves of PK from either species and no effects on PFK Vmax or kinetic constants. Trimethylamine oxide neither affected enzyme activity directly or changed enzyme response to urea. By contrast, high KCl (200 mM) lowered the Vmax of toad PFK and of PK from both species and altered the Km values for both substrates of frog PFK. Other cations were even more inhibitory; for example, the Vmax of PK from either species was reduced by more than 80% by the addition of 200 mM NH4Cl, NaCl, CsCi, or LiCl. High KCl also significantly changed the Km values for substrates of toad lactate dehydrogenase and strongly reduced the Vmax of glutamate dehydrogenase and NAD-dependent isocitrate dehydrogenase in both species whereas 300 mM urea had relatively little effect on these enzymes. The perturbing effect of urea on enzymes and the counteracting effect of trimethylamines that has been reported for elasmobranch fishes (that maintain high concentrations of both solutes naturally) does not appear to apply to amphibian enzymes. Rather, we found that urea is largely a non-perturbing solute for anuran enzymes (I50 values were>1 M for both PK and PFK in both species) and we propose that its accumulation in high concentrations during estivation helps to minimize the increase in cellular ionic strength that would otherwise occur during desiccation and to alleviate the accompanying negative effects of high salt on individual enzyme activities and overall metabolic regulation.

Catégories Science-Metrix
  • 1 - health sciences
  • 2 - biomedical research
  • 3 - biochemistry & molecular biology
Catégories INIST
  • 1 - sciences appliquees, technologies et medecines
  • 2 - sciences biologiques et medicales
  • 3 - sciences biologiques fondamentales et appliquees. psychologie
  • 4 - vertebres: reproduction
Catégories Scopus
  • 1 - Life Sciences ; 2 - Biochemistry, Genetics and Molecular Biology ; 3 - Cell Biology
  • 1 - Life Sciences ; 2 - Biochemistry, Genetics and Molecular Biology ; 3 - Clinical Biochemistry
  • 1 - Life Sciences ; 2 - Biochemistry, Genetics and Molecular Biology ; 3 - Molecular Biology
  • 1 - Health Sciences ; 2 - Medicine ; 3 - General Medicine
Catégories WoS
  • 1 - science ; 2 - cell biology
Identifiant ISTEX

Molecular and Cellular Biochemistry

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  • Batraciens
  • Poissons
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