Control of the removal of reducing equivalents from the cytosol in perfused rat liver.
Control of the removal of reducing equivalents from the cytosol in perfused rat liver.
复制标题
控制灌注大鼠肝脏细胞质中还原当量的去除。
DOI：
10.1016/s0021-9258(19)45823-7
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发表时间：
1971
期刊：
影响因子：
--
通讯作者：
C. Refino
中科院分区：
文献类型：
--
作者：
J. Williamson;A. Jakob;C. Refino
先前采用的大鼠肝脏灌注适合于流通系统，其中收集流出物灌注介质的样品，以通过馏分收集器以2分钟的间隔测量代谢产物。过夜禁食大鼠用于避免内源性糖原形成葡萄糖的并发症。由于木糖醇通过肝脏转化为葡萄糖和乳酸盐与胞质溶胶中NADH的产生有关，因此这些代谢终产物的产生速率可用于提供NADH产生和利用速率的量度。木糖醇代谢主要是氰化物敏感的，显示出线粒体呼吸的强制性参与，以从胞质溶胶中去除还原当量。通过输注细胞溶质或线粒体NAD-连接的脱氢酶的氧化或还原配偶体（例如乙醇、β-羟基丁酸酯）或特异性抑制剂（如鱼藤酮、异戊巴比妥、氰化物和转氨酶抑制剂氨氧基乙酸），研究了各种穿梭体参与还原当量转运至线粒体的情况。通过输注2，4-二硝基苯酚以产生氧化磷酸化的解偶联，鸟氨酸加氨以提供线粒体ATP的能量消耗，研究表明，木糖醇的代谢不受NAD活性的控制，木糖醇脱氢酶，但由NADH的再氧化速率。这一过程受还原当量转移到线粒体的速率和电子流到氧的速率的调节。获得的证据表明，参与NAD和黄素连接的穿梭在整体运输的还原当量从胞质到线粒体。与黄素连接的穿梭体可以与α-甘油磷酸穿梭体进行鉴定，后者通过木糖醇代谢期间产生的异常高的细胞溶质α-甘油磷酸浓度来发挥作用。由木糖醇形成的葡萄糖对氨氧基乙酸和β-羟基丁酸的敏感性表明NAD连接的苹果酸-天冬氨酸穿梭体的参与。这些研究结果的相关性，以控制乙醇利用的肝脏进行了讨论。
The rat liver perfusion previously employed was adapted to a flow-through system in which samples of effluent perfusion medium were collected for measurement of metabolic products at 2-min intervals by means of a fraction collector. Overnight fasted rats were used to avoid complications of glucose formation from endogenous glycogen. Since xylitol conversion to glucose and lactate by the liver is associated with the production of NADH in the cytosol, the rates of production of these metabolic end products can be used to provide a measure of the rate of NADH production and utilization.Xylitol metabolism was predominantly cyanide sensitive showing an obligatory involvement of mitochondrial respiration for removal of reducing equivalents from the cytosol. The participation of various shuttles for the transport of reducing equivalents into the mitochondria was investigated by infusion of the oxidized or reduced partners of cytosolic or mitochondrial NAD-linked dehydrogenases (e.g.ethanol, β-hydroxybutyrate), or specific inhibitors such as rotenone, amobarbital, cyanide, and the transaminase inhibitor aminooxyacetate. The influence of flux in the mitochondrial electron transport chain on the rate of removal of NADH from the cytosol was studied by infusion of 2,4-dinitrophenol to produce an uncoupling of oxidative phosphorylation, ornithine plus ammonia to provide an energy drain on mitochondrial ATP, and artificial electron acceptors to bypass rate-limiting electron transport steps.The studies show that xylitol metabolism was not controlled by the activity of NAD-xylitol dehydrogenase but by the rate of reoxidation of NADH. This process was regulated by the rate of transfer of reducing equivalents into the mitochondria and by the rate of electron flux to oxygen. Evidence was obtained for the participation of both NAD- and flavin-linked shuttles in the over-all transport of reducing equivalents from cytosol to mitochondria. The flavin-linked shuttle may be identified with the α-glycerophosphate shuttle which operates by virtue of the abnormally high cytosolic α-glycerophosphate concentration produced during xylitol metabolism. Involvement of the NAD-linked malate-aspartate shuttle was shown by the sensitivity of glucose formation from xylitol to aminooxyacetate and β-hydroxybutyrate. The relevance of these findings to the control of ethanol utilization by the liver is discussed.