Department of Biology, Institute of Biochemistry, Carleton University, Ottawa, Ontario, Canada.
Cell Biochem Funct. 2022 Jul;40(5):491-500. doi: 10.1002/cbf.3710. Epub 2022 May 23.
The wood frog (Rana sylvatica) undergoes numerous changes to its physiology and metabolic processes to survive the winter months, including adaptations that let them endure whole-body freezing. The regulation of key enzymes of central carbohydrate metabolism in the liver plays a crucial role in mediating the synthesis and maintenance of high concentrations of glucose as a cryoprotectant during freezing as well as glucose reconversion to glycogen after thawing. The present study characterized the regulation of fructose-1,6-bisphosphatase (FBPase; EC 3.1.3.11) from wood frog liver during freezing, FBPase being a crucial enzyme regulating gluconeogenesis. Liver FBPase was purified to homogeneity from control and frozen wood frogs by a one-step chromatographic process. Kinetic and regulatory parameters of the enzyme were investigated and demonstrated a significant decrease in sensitivity to its substrate fructose-1,6-bisphosphate in the liver of frozen frogs, as compared with controls. Immunoblotting also revealed freeze-responsive changes in posttranslational modifications with a significant decrease in serine phosphorylation (by 53%) for FBPase from frozen frogs. Taken together, these results suggest that FBPase is suppressed, and gluconeogenesis is inhibited during freezing. This response acts as an important component of the metabolic survival strategy of the wood frog.
林蛙（Rana sylvatica）通过对生理机能和代谢过程的诸多改变来适应冬季，包括让它们能忍受全身冻结的适应能力。肝脏中中枢碳水化合物代谢关键酶的调节在介导冷冻过程中葡萄糖作为防冻保护剂的合成和维持以及解冻后葡萄糖向糖原的再转化方面发挥着关键作用。本研究描述了林蛙肝脏中果糖-1,6-二磷酸酶（FBPase；EC 3.1.3.11）在冻结过程中的调节，FBPase 是调节糖异生的关键酶。通过一步色谱过程从对照和冷冻林蛙肝脏中均一地纯化了 FBPase。研究了该酶的动力学和调节参数，并表明与对照相比，冷冻青蛙肝脏中该酶对其底物果糖-1,6-二磷酸的敏感性显著降低。免疫印迹也显示出翻译后修饰的冷冻应答变化，FBPase 的丝氨酸磷酸化显著降低（降低 53%）。总之，这些结果表明，FBPase 受到抑制，糖异生在冻结过程中受到抑制。这种反应是林蛙代谢生存策略的重要组成部分。
