New Insights to Regulation of Fructose-1,6-bisphosphatase during Anoxia in Red-Eared Slider, Trachemys scripta elegans

Abstract

The red-eared slider (Trachemys scripta elegans) undergoes numerous changes to its physiological and metabolic processes to survive without oxygen. During anoxic conditions, its metabolic rate drops drastically to minimize energy requirements. The alterations in the central metabolic pathways are often accomplished by the regulation of key enzymes. The regulation of one such enzyme, fructose-1,6-bisphosphatase (FBPase; EC 3.1.3.11), was characterized in the present study during anoxia in liver. FBPase is a crucial enzyme of gluconeogenesis. The FBPase was purified from liver tissue in both control and anoxic conditions and subsequently assayed to determine the kinetic parameters of the enzyme. The study revealed the relative degree of post-translational modifications in the FBPase from control and anoxic turtles. Further, this study demonstrated a significant decrease in the maximal activity in anoxic FBPase and decreased sensitivity to its substrate fructose-1,6-bisphosphate (FBP) when compared to the control. Immunoblotting demonstrated increased threonine phosphorylation (~1.4-fold) in the anoxic FBPase. Taken together, these results suggest that the phosphorylation of liver FBPase is an important step in suppressing FBPase activity, ultimately leading to the inhibition of gluconeogenesis in the liver of the red-eared slider during anaerobic conditions.

One‐step purification and regulation of fructose 1,6‐bisphosphatase from the liver of the freeze‐tolerant wood frog, Rana sylvatica

“…The results obtained here correspond well with the findings of previous studies of FBPase in support of metabolic rate depression as a primary mechanism of surviving freezing and other environmental stresses. For example, Bell and Storey 37 reported suppression of skeletal muscle FBPase activity during ground squirrel hibernation and another study on red‐eared slider turtles ( Trachemys scripta elegans ) showed negative regulation of liver FBPase under anoxia, ultimately leading to inhibition of gluconeogenesis 38 …”

“…For example, Bell and Storey 37 reported suppression of skeletal muscle FBPase activity during ground squirrel hibernation and another study on redeared slider turtles (Trachemys scripta elegans) showed negative regulation of liver FBPase under anoxia, ultimately leading to inhibition of gluconeogenesis. 38 FBPase is a regulatory enzyme in carbohydrate metabolism, and along with PFK-1, controls an important locus in glycolysis/ gluconeogenesis that interconverts hexose phosphates and triose phosphates. When active, FBPase facilitates gluconeogenic flux whereas it is inactivated via the actions of allosteric inhibitors ADP, AMP, and F26BP [39][40][41] and covalent modifications [41][42][43] when glycolysis is activated.…”

Metabolic regulation of endothelial senescence

“…Glycolysis begins with the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate (FBP) catalyzed by the aldolase enzyme. FBP plays a crucial role not only in glycolysis but also in gluconeogenesis and the PPP ( Figure 1 ) ( 43 , 44 ). Gluconeogenesis is the process of de novo glucose synthesis from available precursors, which plays a crucial role in maintaining glucose homeostasis to meet energy demands, particularly during prolonged starvation in animals ( 45 ).…”

Differential Expression of Gluconeogenesis-Related Transcripts in a Freshwater Zooplankton Model Organism Suggests a Role of the Cori Cycle in Hypoxia Tolerance

“…The role of the Cori cycle or gluconeogenesis (GNG) has been well characterized in humans and other mammals, where products of glycolysis are utilized in the liver to resupply muscles and other critical tissues with glucose and NAD+, thus allowing glycolysis to continuously generate ATP during bursts of muscular activity or while in hypoxic or fasting conditions [1][2][3][4][5][6]. In some other vertebrates adapted to either periodic fasting [7] or hypoxia [8], the Cori cycle emerges as a key element of adaptation to environmental extremes.…”