BRAIN ALPHA-KETOGLUTARATE DEHYDROGENASE COMPLEX - KINETIC-PROPERTIES, REGIONAL DISTRIBUTION, AND EFFECTS OF INHIBITORS
BRAIN ALPHA-KETOGLUTARATE DEHYDROGENASE COMPLEX - KINETIC-PROPERTIES, REGIONAL DISTRIBUTION, AND EFFECTS OF INHIBITORS
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DOI：
10.1111/j.1471-4159.1986.tb00768.x
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发表时间：
1986-11-01
影响因子：
4.7
通讯作者：
COOPER, AJL
中科院分区：
文献类型：
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作者：
LAI, JCK;COOPER, AJL
研究了纯化的大鼠脑线粒体中α-酮戊二酸脱氢酶复合物(KGDHC；EC 1.2.4.2、EC 2.3.1.6和EC 1.6.4.3)的底物和辅因子需求以及一些动力学特性。在本研究中采用的测定条件下，脑线粒体KGDHC显示出对α-酮戊二酸、CoA和NAD的绝对需要，并且仅部分需要添加的焦磷酸硫胺素，但不需要Mg 2+ 。最适pH值在7.2和7.4之间，但是，当pH值低于7.0或高于7.8时，KGDHC活性显着下降。各脑区的KGDHC活动遵循等级顺序；大脑皮层 > 小脑 .gtoreq.中脑 > 纹状体 = 海马 > 下丘脑 > 脑桥和延髓 > 嗅球。在病理浓度的氨 (0.2-2 mM) 下，脑线粒体 KGDHC 受到显着抑制。然而，纯化的牛心 KGDHC 和分离的大鼠心脏线粒体中的 KGDHC 活性对抑制的敏感性要低得多。在5mM时，β-亚甲基-DL-天冬氨酸和DL-乙烯基甘氨酸（脑葡萄糖氧化抑制剂）抑制纯化的心脏，但不抑制脑线粒体酶复合物。在大约10μM时，钙轻微刺激（10-15%）脑线粒体KGDHC。在浓度高于 100 μM 时，钙 (IC50 = 1 mM) 抑制脑线粒体和纯化的心脏 KGDHC。目前的结果表明，大鼠脑线粒体 KGDHC 的一些动力学特性与纯化的牛心脏和大鼠心脏线粒体酶复合物的动力学特性不同。他们还表明，氨对 KGDHC 的抑制以及随后对柠檬酸循环通量的影响可能在高氨血症和以高氨血症为一致特征的疾病（例如肝性脑病、先天性尿素代谢缺陷、雷氏综合征）中具有病理生理学和/或致病性重要性。脑内钙积聚发生在多种病理状况下。因此，这种钙积累可能对 KGDHC 活性产生有害影响。
The substrate and cofactor requirements and some kinetics properties of the .alpha.-ketoglutarate dehydrogenase complex (KGDHC; EC 1.2.4.2, EC 2.3.1.6, and EC 1.6.4.3) in purified rat brain mitochondria were studied. Brain mitochondrial KGDHC showed absolute requirement for .alpha.-ketoglutarate, CoA and NAD, and only partial requirement for added thiamine pyrophosphate, but not requirement for Mg2+ under the assay conditions employed in this study. The pH optimum was between 7.2 and 7.4, but, at pH values below 7.0 or above 7.8, KGDHC activity decreased markedly. KGDHC activity in various brain regions followed the rank order; cerebral cortex > cerebellum .gtoreq. midbrain > striatum = hippocampus > hypothalamus > pons and medulla > olfactory bulb. Significant inhibition of brain mitochondrial KGDHC was noted at pathological concentrations of ammonia (0.2-2 mM). However, the purified bovine heart KGDHC and KGDHC activity in isolated rat heart mitochondria were much less sensitive to inhibition. At 5 mM both .beta.-methylene-DL-aspartate and DL-vinylglycine (inhibitors of cerebral glucose oxidation) inhibited the purified heart but not the brain mitochondrial enzyme complex. At approximately 10 .mu.M, calcium slightly stimulated (by 10-15%) the brain mitochondrial KGDHC. At concentrations above 100 .mu.M, calcium (IC50 = 1 mM) inhibited both brain mitochondrial and purified heart KGDHC. The present results suggest that some of the kinetic properties of the rat brain mitochondrial KGDHC differ from those of the purified bovine heart and rat heart mitochondrial enzyme complexes. They also suggest that the inhibition of KGDHC by ammonia and the consequent effect on the citric acid cycle fluxes may be of pathophysiological and/or pathogenic importance in hyperammonemia and in disease (e.g., hepatic encephalopathy, inborn errors of urea metabolism, Reye''s sydrome) where hyperammonemia is a consistent feature. Brain accumulation of calcium occurs in a number of pathological conditions. Therefore, it is possible that such a calcium accumulation may have a deleterious effect on KGDHC activity.