Effects of anoxia exposure and aerobic recovery on metabolic enzyme activities in the freshwater turtle <i>Trachemys scripta elegans</i>

Abstract

The effects of anoxic submergence (20 h at 7°C in nitrogen-bubbled water) and subsequent aerobic recovery (24 h at 7°C) on the maximal activities of 21 metabolic enzymes were assessed in liver, kidney, heart, brain, and red and white skeletal muscle of an anoxia-tolerant freshwater turtle, the red-eared slider, Trachemys scripta elegans. Anoxia exposure affected the activities of only a few enzymes; for example, it reduced the activity of phosphofructokinase in liver and brain, hexokinase in kidney, glycerol-3-phosphate dehydrogenase and glutamate-oxaloacetate transaminase in heart, glutamate dehydrogenase and serine dehydratase in brain, and 3-hydroxyacyl-CoA dehydrogenase in red muscle. During aerobic recovery, activities of most of these enzymes rebounded and activities of 10 others that were not affected by anoxia rose during recovery. Anoxia-induced changes in selected enzymes appear to meet very specific needs such as glycolytic-rate depression, regulation of glycolytic versus gluconeogenic flux in liver, or alterations in amino acid neurotransmitter levels in brain. Overall, the data demonstrate that the enzymatic make-up of turtle organs undergoes very few changes during anoxia exposure and recovery, which shows that the constitutive activities of enzymes are well designed to meet the metabolic demands of anoxic excursions.Résumé : Nous avons évalué les effets d'une submersion anoxique (20 h à 7°C, dans de l'eau où barbotait de l'azote) et de la récupération aérobie subséquente (24 h à 7°C) sur l'activité maximale de 21 enzymes métaboliques dans le foie, les reins, le coeur, le cerveau, ainsi que dans les muscles squelettiques blanc et rouge d'une tortue d'eau douce tolérant l'anoxie, Trachemys scripta elegans. L'exposition aux conditions anoxiques affecte l'activité de seulement quelques enzymes : par exemple, celle de la phosphofructokinase est réduite dans le foie et dans le cerveau, celle de l'hexokinase dans le rein, celle de la glycérol-3-phosphate déshydrogénase et de la glutamate-oxaloacétate transaminase dans le coeur, celle de la glutamate-déshydrogénase et de la sérine déshydratase dans le cerveau, enfin celle de la 3-hydroxyacyl-CoA déshydrogénase dans le muscle rouge. Durant la récupération en conditions aérobies, l'activité de la plupart de ces enzymes reprend et l'activité de 10 autres enzymes non affectées par l'anoxie augmente. Les changements dans l'activité de certaines enzymes particulières générés par l'exposition à l'anoxie semblent répondre à des besoins spécifiques comme, par exemple, la diminution du taux de glycolyse, la régulation du flux glycolytique par rapport au flux gluconéogénique dans le foie, ou des modifications des concentrations des acides aminés neurotransmetteurs dans le cerveau. Dans l'ensemble, ces données démontrent que le complexe enzymatique des organes de la tortue subit peu de changements au cours d'une exposition à l'anoxie et de la période de récupération subséquente, ce qui veut dire que les activités constitutives des enzymes sont aptes à répondre aux exi...

Characterization of Fructose-1,6-Bisphosphate Aldolase during Anoxia in the Tolerant Turtle, Trachemys scripta elegans: An Assessment of Enzyme Activity, Expression and Structure

“…Previous studies have explored the importance of regulating glycolytic enzymes during anoxia exposure in T. s. elegans [9]–[11]. These studies have documented significant changes in both enzyme kinetics and activity upon prolonged exposure to anoxia.…”

“…Regulated liver enzymes involved in glycolysis include: phosphofructokinase (PFK), demonstrating a 3-fold decrease in the I 50 value for citrate and a 1.5-fold increase in the K m value for ATP during anoxia [9]; pyruvate kinase (PK), which demonstrated an anoxia responsive 1.5-fold increase in the I 50 for alanine and a 1.2-fold increase in maximal activity [9]; lactate dehydrogenase (LDH), displaying an increase in the K m value for pyruvate at various temperature and pH conditions, a decrease in the maximal activity (1.6-fold) in the lactate producing direction and a decrease in the I 50 for pyruvate at various temperature and pH conditions during exposure to anoxia [10]. Furthermore, a comprehensive study of 20 enzymes involved in intermediary metabolism showed multiple changes in activities due to prolonged exposure to anoxia [11]. These studies suggest that global control of glycolytic enzymes during bouts of anoxia seem to be paramount in the adaptation of T. s. elegans to anoxic stress.…”