Institute of Biochemistry & Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6, Canada.
Institute of Biochemistry & Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6, Canada.
Comp Biochem Physiol B Biochem Mol Biol. 2020 Oct-Nov;248-249:110466. doi: 10.1016/j.cbpb.2020.110466. Epub 2020 Jun 24.
The Richardson's ground squirrel (Urocitellus richardsonii) undergoes numerous changes to its core physiological and metabolic processes over the months it spends hibernating during the winter. Winter torpor is characterized by an overall reduction in metabolic rate, a lowering of core body temperature, and a switch to preferential consumption of lipids instead of carbohydrates. The alterations in central metabolic pathways are often accomplished by the regulation of key enzymes within the glycolytic pathway. The regulation of one such enzyme, pyruvate kinase (PK), was characterized in the present study in the liver of torpid ground squirrels. PK was purified from liver tissue of euthermic and hibernating U. richardsonii and subsequently assayed to determine the kinetic parameters of the enzyme at 22° and 5 °C. Additional studies assessed the relative degree of post-translational modifications in PK from control and hibernating ground squirrels. The results from this study demonstrated significantly lowered maximal activity in the hibernating form of the enzyme and decreased sensitivity to the activator FBP when compared to the control. Immunoblotting demonstrated increased relative serine and threonine phosphorylation (~3 fold) in the hibernating PK. Taken together these results suggest that phosphorylation of liver PK is an important step in inhibiting glycolytic activity in the liver of the Richardson's ground squirrel during torpor.
冬季休眠期间，理查森地松鼠（Urocitellus richardsonii）的核心生理和代谢过程会发生许多变化。冬季休眠的特点是代谢率总体降低，核心体温降低，以及优先消耗脂肪而不是碳水化合物。中央代谢途径的改变通常通过糖酵解途径中的关键酶的调节来实现。本研究中对休眠地松鼠肝脏中的一种关键酶——丙酮酸激酶（PK）的调节进行了表征。PK 从冬眠和非冬眠的 U. richardsonii 的肝组织中纯化出来，并随后进行了测定，以确定该酶在 22°C 和 5°C 时的动力学参数。进一步的研究评估了 PK 从对照和冬眠地松鼠中的翻译后修饰的相对程度。这项研究的结果表明，与对照相比，酶的休眠形式的最大活性显著降低，并且对激活剂 FBP 的敏感性降低。免疫印迹显示，冬眠 PK 的丝氨酸和苏氨酸磷酸化程度增加了约 3 倍。综合这些结果表明，磷酸化肝脏 PK 是在理查森地松鼠休眠期间抑制肝脏糖酵解活性的重要步骤。
