Control mechanisms of gluconeogenesis and ketogenesis. I. Effects of oleate on gluconeogenesis in perfused rat liver.
Control mechanisms of gluconeogenesis and ketogenesis. I. Effects of oleate on gluconeogenesis in perfused rat liver.
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糖异生和酮生成的控制机制。
DOI：
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发表时间：
1969
影响因子：
4.8
通讯作者：
R. Scholz
中科院分区：
文献类型：
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作者：
J. Williamson;E. Browning;R. Scholz
本文研究了油酸（1.0 ~ 1.5mm）对以丙氨酸（5 ~ 10 mm）、l（+）-乳酸（8 ~ 12 mm）、丙酮酸（1.5 ~ 2.0mm）或二羟丙酮（10 mm）为致肝损害前体的禁食大鼠肝脏的影响。在用丙氨酸、乳酸或丙酮酸灌注的对照肝脏中，葡萄糖产生速率分别为60、120和95 μ mol/100 g体重/小时。油酸盐将这些速率增加到132、250和194微摩尔/100 g体重/小时。以乳酸盐为底物，葡萄糖的形成占60%和78%的乳酸盐的摄取在不存在和存在的油酸。以丙酮酸为底物，在存在和不存在油酸的情况下，肝脏吸收的丙酮酸约有一半转化为葡萄糖。以二羟基丙酮为底物，葡萄糖的产生速率为每小时每100 g体重250 µ mol，油酸盐不会进一步增加葡萄糖的产生速率。这表明异戊糖生成的速率控制步骤先于磷酸丙糖的形成。油酸增加了线粒体和胞质空间中吡啶核苷酸系统的还原状态，如乳酸与丙酮酸、β-羟基丁酸与乙酰乙酸和苹果酸与乙酰乙酸的比率增加所示。油酸盐给药后，还原型吡啶核苷酸的总组织水平也增加。为了确定酶序列中相互作用的位点，对产酶途径的代谢中间产物进行了测量。这些相互作用的意义进行了分析的交叉定理。甘油醛-3-P脱氢酶仅以丙氨酸为底物作为对照位点。有人提出，这一反应是刺激的升高的NADH：NAD+的比例保持在细胞质中的脂肪酸氧化增强。以乳酸盐和丙酮酸盐为底物，在丙酮酸羧化酶（激活）和磷酸果糖激酶（抑制）处观察到对照位点。这些效应被解释为是由乙酰辅酶A和柠檬酸盐水平升高引起的。果糖-1，6-二-P和果糖-6-P之间的相互作用被解释为指示这些中间体的再循环，其至少与油酸酯添加后观察到的增加的葡萄糖通量一样快。这导致ATP的浪费使用，但可能不超过耗氧量的10 - 20%。丙酮酸羧化的控制被认为代表了脂肪酸氧化和脂肪异生之间最具生理意义的相互作用。
Abstract The effects of oleate (1.0 to 1.5 mm) were studied in livers from fasted rats perfused with alanine (5 to 10 mm), l(+)-lactate (8 to 12 mm), pyruvate (1.5 to 2.0 mm), or dihydroxyacetone (10 mm) as gluconeogenic precursors. Rates of glucose production in control livers perfused with alanine, lactate, or pyruvate were 60, 120, and 95 µmoles per 100 g, body weight, per hour, respectively. Oleate increased these rates to 132, 250, and 194 µmoles per 100 g, body weight, per hour with the three substrates. With lactate as substrate, glucose formation accounted for 60% and 78% of the lactate uptake in the absence and presence of oleate. With pyruvate as substrate, about half of the pyruvate taken up by the liver was converted to glucose, both in the presence and absence of oleate. With dihydroxyacetone as substrate, the rate of glucose production was 250 µmoles per 100 g, body weight, per hour, and was not increased further by oleate. This indicates that the rate-controlling step of gluconeogenesis is prior to the formation of triose phosphates. Oleate increased the state of reduction of the pyridine nucleotide systems in both mitochondrial and cytosolic spaces as shown by increases in the ratios of lactate to pyruvate, β-hydroxybutyrate to acetoacetate, and malate to oxalacetate. Total tissue levels of the reduced forms of the pyridine nucleotides also increased after oleate administration. Measurements of metabolic intermediates of the gluconeogenic pathway were made in order to identify sites of interaction in the enzyme sequence. The significance of these interactions was analyzed by the crossover theorem. Glyceraldehyde-3-P dehydrogenase appeared as a control site only with alanine as substrate. It is proposed that this reaction was stimulated by the elevated NADH:NAD+ ratio maintained in the cytosol during enhanced fatty acid oxidation. With lactate and pyruvate as substrates, control sites were observed at pyruvate carboxylase (activation) and phosphofructokinase (inhibition). These effects were interpreted as being caused by elevated levels of acetyl coenzyme A and citrate. The interaction between fructose-1,6-di-P and fructose-6-P is interpreted as indicating recycling of these intermediates, which is at least as rapid as the increased glucose flux observed after oleate addition. This results in a wasteful use of ATP, but probably represents no more than 10 to 20% of the oxygen consumption. Control of pyruvate carboxylation is considered to represent the most physiologically meaningful interaction between fatty acid oxidation and gluconeogenesis.