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

The effects of anoxic submergence (20 h at 7 degreesC in nitrogen-bubbled w ater) and subsequent aerobic recovery (24 h at 7 degreesC) on the maximal a ctivities of 21 metabolic enzymes were assessed in liver, kidney, heart, br ain, and red and white skeletal muscle of an anoxia-tolerant freshwater tur tle, the red-eared slider, Trachemys scripta elegans. Anoxia exposure affec ted the activities of only a few enzymes; for example, it reduced the activ ity of phosphofructokinase in liver and brain, hexokinase in kidney, glycer ol-3-phosphate dehydrogenase and glutamate-oxaloacetate transaminase in hea rt, glutamate dehydrogenase and serine dehydratase in brain, and 3-hydroxya cyl-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 depress ion, regulation of glycolytic versus gluconeogenic flux in liver, or altera tions in amino acid neurotransmitter levels in brain. Overall, the data dem onstrate that the enzymatic make-up of turtle organs undergoes very few cha nges during anoxia exposure and recovery, which shows that the constitutive activities of enzymes are well designed to meet the metabolic demands of a noxic excursions.