Harris R A, Popov K M, Zhao Y, Kedishvili N Y, Shimomura Y, Crabb D W
Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis 46202, USA.
Adv Enzyme Regul. 1995;35:147-62. doi: 10.1016/0065-2571(94)00020-4.
Molecular cloning has provided evidence for a new family of protein kinases in eukaryotic cells. These kinases show no sequence similarity with other eukaryotic protein kinases, but are related by sequence to the histidine protein kinases found in prokaryotes. These protein kinases, responsible for phosphorylation and inactivation of the branched-chain alpha-ketoacid dehydrogenase and pyruvate dehydrogenase complexes, are located exclusively in mitochondrial matrix space and have most likely evolved from genes originally present in respiration-dependent bacteria endocytosed by primitive eukaryotic cells. Long-term regulatory mechanisms involved in the control of the activities of these two kinases are of considerable interest. Dietary protein deficiency increases the activity of branched-chain alpha-ketoacid dehydrogenase kinase associated with the branched-chain alpha-ketoacid dehydrogenase complex. The amount of branched-chain alpha-ketoacid dehydrogenase kinase protein associated with the branched-chain alpha-ketoacid dehydrogenase complex and the message level for branched-chain alpha-ketoacid dehydrogenase kinase are both greatly increased in the liver of rats starved for protein, suggesting increased expression of the gene encoding branched-chain alpha-ketoacid dehydrogenase kinase. The increase in branched-chain alpha-ketoacid dehydrogenase kinase activity results in greater phosphorylation and lower activity of the branched-chain alpha-ketoacid dehydrogenase complex. The metabolic consequence is conservation of branched chain amino acids for protein synthesis during periods of dietary protein deficiency. Two isoforms of pyruvate dehydrogenase kinase have been identified and cloned. Pyruvate dehydrogenase kinase 1, the first isoform cloned, corresponds to the 48 kDa subunit of the pyruvate dehydrogenase kinase isolated from rat heart tissue. Pyruvate dehydrogenase kinase 2, the second isoform cloned, corresponds to the 45 kDa subunit of this enzyme. In addition, it also appears to correspond to a possibly free or soluble form of pyruvate dehydrogenase kinase that was originally named kinase activator protein. Assuming that differences in kinetic and/or regulatory properties of these isoforms exist, tissue specific expression of these enzymes and/or control of their association with the complex will probably prove to be important for the long term regulation of the activity of the pyruvate dehydrogenase complex. Starvation and the diabetic state are known to greatly increase activity of the pyruvate dehydrogenase kinase in the liver, heart and muscle of the rat. This contributes in these states to the phosphorylation and inactivation of the pyruvate dehydrogenase complex and conservation of pyruvate and lactate for gluconeogenesis.(ABSTRACT TRUNCATED AT 400 WORDS)
分子克隆为真核细胞中一个新的蛋白激酶家族提供了证据。这些激酶与其他真核蛋白激酶没有序列相似性，但在序列上与原核生物中发现的组氨酸蛋白激酶相关。这些蛋白激酶负责支链α-酮酸脱氢酶和丙酮酸脱氢酶复合物的磷酸化和失活，仅位于线粒体基质空间，很可能是从原始真核细胞内吞的依赖呼吸的细菌中最初存在的基因进化而来。控制这两种激酶活性的长期调节机制备受关注。饮食蛋白质缺乏会增加与支链α-酮酸脱氢酶复合物相关的支链α-酮酸脱氢酶激酶的活性。在蛋白质饥饿的大鼠肝脏中，与支链α-酮酸脱氢酶复合物相关的支链α-酮酸脱氢酶激酶蛋白量以及支链α-酮酸脱氢酶激酶的信使水平都大大增加，这表明编码支链α-酮酸脱氢酶激酶的基因表达增加。支链α-酮酸脱氢酶激酶活性的增加导致支链α-酮酸脱氢酶复合物的磷酸化增加和活性降低。代谢结果是在饮食蛋白质缺乏期间将支链氨基酸保留用于蛋白质合成。已鉴定并克隆了丙酮酸脱氢酶激酶的两种同工型。丙酮酸脱氢酶激酶1是克隆的第一种同工型，对应于从大鼠心脏组织中分离出的丙酮酸脱氢酶激酶的48 kDa亚基。丙酮酸脱氢酶激酶2是克隆的第二种同工型，对应于该酶的45 kDa亚基。此外，它似乎还对应于最初称为激酶激活蛋白的丙酮酸脱氢酶激酶的一种可能游离或可溶形式。假设这些同工型在动力学和/或调节特性上存在差异，这些酶的组织特异性表达和/或它们与复合物的结合控制可能对丙酮酸脱氢酶复合物活性的长期调节很重要。已知饥饿和糖尿病状态会大大增加大鼠肝脏、心脏和肌肉中丙酮酸脱氢酶激酶的活性。在这些状态下，这会导致丙酮酸脱氢酶复合物的磷酸化和失活，并保留丙酮酸和乳酸用于糖异生。（摘要截短至400字）
