The citric acid cycle (CAC) is a central metabolic pathway that links carbohydrate, lipid, and amino acid metabolism in the mitochondria and, hence, is a crucial target for metabolic regulation. The α-ketoglutarate dehydrogenase complex (KGDC) is the rate-limiting step of the CAC, the three enzymes of the complex catalyzing the transformation of α-ketoglutarate to succinyl-CoA with the release of CO2 and reduction of NAD to NADH. During hibernation, the metabolic rate of small mammals is suppressed, in part due to reduced body temperature but also active controls that suppress aerobic metabolism. The present study examined KGDC regulation during hibernation in skeletal muscle of the Richardson's ground squirrel (Urocitellus richardsonii). The KGDC was partially purified from skeletal muscle of euthermic and hibernating ground squirrels and kinetic properties were evaluated at 5°, 22°, and 37 °C. KGDC from hibernator muscle at all temperatures compared with euthermic controls exhibited a decreased affinity for CoA as well as reduced activation by Ca2+ ions at 5 °C from both euthermic and hibernating conditions. Co-immunoprecipitation was employed to isolate the E1, E2 and E3 enzymes of the complex (OGDH, DLST, DLD) to allow immunoblot analysis of post-translational modifications (PTMs) of each enzyme. The results showed elevated phospho-tyrosine content on all three enzymes during hibernation as well as increased ADP-ribosylation and succinylation of hibernator OGDH. Taken together these results show that the KGDC is regulated by posttranslational modifications and temperature effects to reorganize enzyme activity and mitochondrial function to aid suppression of mitochondrial activity during hibernation.

中文翻译：

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在小型哺乳动物（理查森的地松鼠（Urocitellus richardsonii））的休眠状态下调节α-酮戊二酸脱氢酶复合物。

柠檬酸循环（CAC）是连接线粒体中碳水化合物，脂质和氨基酸代谢的主要代谢途径，因此，它是代谢调节的关键靶标。α-酮戊二酸脱氢酶复合物（KGDC）是CAC的限速步骤，该复合物的三种酶催化α-酮戊二酸转化为琥珀酰辅酶A，并释放出CO2和将NAD还原为NADH。在冬眠期间，小哺乳动物的代谢率受到抑制，部分原因是体温降低，但也有抑制有氧代谢的主动控制。本研究检查了理查森地松鼠（Urocitellus richardsonii）的骨骼肌冬眠期间的KGDC调节。从中性和冬眠松鼠的骨骼肌中部分纯化KGDC，并在5°，22°和37°C下评估动力学性能。与正常对照相比，在所有温度下来自冬眠肌的KGDC表现出对CoA的亲和力降低，并且在正常条件下和冬眠条件下，在5°C时对Ca2 +离子的活化作用均降低。使用共免疫沉淀法分离复合物（OGDH，DLST，DLD）的E1，E2和E3酶，以便对每种酶的翻译后修饰（PTM）进行免疫印迹分析。结果显示，冬眠期间OGDH的所有三种酶的磷酸酪氨酸含量增加，ADP核糖基化和琥珀酰化增加。