Effects of anoxia exposure and aerobic recovery on metabolic enzyme activities in the freshwater turtleTrachemys scripta elegans

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.