REDOX STATE OF FREE NICOTINAMIDE-ADENINE DINUCLEOTIDE PHOSPHATE IN CYTOPLASM OF RAT LIVER
REDOX STATE OF FREE NICOTINAMIDE-ADENINE DINUCLEOTIDE PHOSPHATE IN CYTOPLASM OF RAT LIVER
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DOI：
10.1042/bj1150609a
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发表时间：
1969-01-01
影响因子：
4.1
通讯作者：
KREBS, HA
中科院分区：
文献类型：
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作者：
VEECH, RL;EGGLESTON, LV;KREBS, HA
1.在冷冻夹持的大鼠肝脏中测量“苹果酸”酶（EC 1.1.1.40）和异柠檬酸脱氢酶（EC 1.1.1.42）的氧化和还原底物的浓度。通过假设这些脱氢酶系统的反应物在细胞质中处于平衡，计算[游离NADP+]/[游离NADPH]比率。假设的理由进行了讨论。2.在不同营养条件下（营养良好，48小时），饥饿、用低碳水化合物饮食喂养、用高蔗糖饮食喂养）都具有相同的数量级，尽管在改变饮食时发生特征性变化。该比率的值下降饥饿和低碳水化合物饮食喂养，并略有上升与高糖饮食喂养。3.该比值的平均值计算为0.001和0.015之间，这比细胞质[游离NAD+]/[游离NADH]比值的值低约100000倍。4.两个烟酰胺腺嘌呤二核苷酸对的氧化还原状态的差异可以在简单的物理化学基础上解释。这些差异是平衡的结果，平衡由许多高活性的易可逆的脱氢酶和转氨酶的平衡常数以及这些酶的底物和产物的浓度决定。5.决定性的特征是NAD和NADP对共享底物的事实。这种共享提供了两对氧化还原状态之间的联系。6.应用Kraupp，Adler-Kastner，Niessner & Plank（1967），Goldberg，Passonneau & Lowry（1966）和Kauffman，Brown，Passonneau & Lowry（1968）发表的数据计算方法表明，心肌细胞质和小鼠脑细胞质中NAD和NADP对的氧化还原状态与大鼠肝脏中的氧化还原状态具有相同的顺序。7.在38°、pH 7·0和I 0·25（计算[游离NADP+]/[游离NADPH]比值所需）下测定平衡常数，得到苹果酸酶的值为3·44×10− 2 m − 1（以CO2而不是HCO 3 −作为反应物），谷胱甘肽还原酶的值为1·98×10− 2 m − 1。
1. The concentrations of the oxidized and reduced substrates of the ‘malic’ enzyme (EC 1.1.1.40) and isocitrate dehydrogenase (EC 1.1.1.42) were measured in freeze-clamped rat livers. By assuming that the reactants of these dehydrogenase systems are at equilibrium in the cytoplasm the [free NADP+]/[free NADPH] ratio was calculated. The justification of the assumption is discussed. 2. The values of this ratio obtained under different nutritional conditions (well-fed, 48hr.-starved, fed with a low-carbohydrate diet, fed with a high-sucrose diet) were all of the same order of magnitude although characteristic changes occurred on varying the diet. The value of the ratio fell on starvation and on feeding with the low-carbohydrate diet and rose slightly on feeding with the high-sucrose diet. 3. The mean values of the ratio were calculated to be between 0·001 and 0·015, which is about 100000 times lower than the values of the cytoplasmic [free NAD+]/[free NADH] ratio. 4. The differences in the redox state of the two nicotinamide–adenine dinucleotide couples can be explained on a simple physicochemical basis. The differences are the result of equilibria that are determined by the equilibrium constants of a number of highly active readily reversible dehydrogenases and transaminases and the concentrations of the substrates and products of these enzymes. 5. The decisive feature is the fact that the NAD and NADP couples share substrates. This sharing provides a link between the redox states of the two couples. 6. The application of the method of calculation to data published by Kraupp, Adler-Kastner, Niessner & Plank (1967), Goldberg, Passonneau & Lowry (1966) and Kauffman, Brown, Passonneau & Lowry (1968) shows that the redox states of the NAD and NADP couples in cardiac-muscle cytoplasm and in mouse-brain cytoplasm are of the same order as those in rat liver. 7. The determination of the equilibrium constant at 38°, pH7·0 andI0·25 (required for the calculation of the [free NADP+]/[free NADPH] ratio), gave a value of 3·44×10−2mfor the ‘malic’ enzyme (with CO2rather than HCO3−as the reactant) and a value of 1·98×10−2m−1for glutathione reductase.