The intertidal marine snail, Littorina littorea, has evolved to survive bouts of anoxia and extracellular freezing brought about by changing tides and subsequent exposure to harsh environmental conditions. Survival in these anoxic conditions depends on the animals entering a state of metabolic rate depression in order to maintain an appropriate energy production-consumption balance during periods of limited oxygen availability. This study investigated the kinetic, physical, and regulatory properties of pyruvate kinase (PK), which catalyzes the final reaction of aerobic glycolysis, from foot muscle of L. littorea to determine if the enzyme is differentially regulated in response to anoxia and freezing exposure. PK purified from foot muscle of anoxic animals exhibited a lower affinity for its substrate phosphoenolpyruvate than PK from control and frozen animals. PK from anoxic animals was also more sensitive to a number of allosteric regulators, including alanine and aspartate, which are key anaerobic metabolites in L. littorea. Furthermore, PK purified from anoxic and frozen animals exhibited greater stability compared to the non-stressed control animals, determined through high-temperature incubation studies. Phosphorylation of threonine and tyrosine residues was also assessed and demonstrated that levels of threonine phosphorylation of PK from anoxic animals were significantly higher than those of PK from control and frozen animals, suggesting a potential mechanism for regulating PK activity. Taken together, these results suggest that PK plays a role in suppressing metabolic rate in these animals during environmental anoxia exposure.

潮间海洋蜗牛Littorina littorea已进化成能忍受因潮汐变化和随后暴露于恶劣环境条件而引起的缺氧和细胞外冻结。在这些缺氧条件下的存活取决于动物进入代谢率降低状态，以便在有限的氧气供应期间维持适当的能量产生-消耗平衡。这项研究调查了丙酮酸激酶（PK）的动力学，物理和调节特性，丙酮酸激酶可催化立特乳杆菌足部肌肉中有氧糖酵解的最终反应。确定该酶是否响应缺氧和冰冻暴露而受到不同的调节。从缺氧动物足部肌肉中纯化的PK与其底物磷酸烯醇丙酮酸的亲和力低于对照和冷冻动物的PK。缺氧动物的PK对多种变构调节剂也更敏感，包括丙氨酸和天冬氨酸，它们是L. littorea中的关键厌氧代谢产物。。此外，通过高温孵育研究确定，与无压力的对照动物相比，从缺氧和冷冻动物纯化的PK表现出更高的稳定性。还评估了苏氨酸和酪氨酸残基的磷酸化，并证明缺氧动物的PK的苏氨酸磷酸化水平显着高于对照和冰冻动物的PK的苏氨酸磷酸化水平，表明调节PK活性的潜在机制。综上所述，这些结果表明在环境缺氧暴露期间，PK在抑制这些动物的代谢率中起作用。