Quantifying the carboxylation of pyruvate in pancreatic islets
Quantifying the carboxylation of pyruvate in pancreatic islets
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DOI：
10.1074/jbc.271.5.2539
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发表时间：
1996-02-02
影响因子：
4.8
通讯作者：
Landau, BR
中科院分区：
文献类型：
--
作者：
Khan, A;Ling, ZC;Landau, BR
据估计，丙酮酸通过羧化作用进入胰岛的柠檬酸循环的程度与脱羧化作用相同或更大。这些估计是假设[1，4-C-14]琥珀酸二甲酯和[2-3-C-14]琥珀酸二甲酯以10 mM的浓度与胰岛孵育，产生相同的(CO2)-C-14产率，就好像已经孵育了[1-C-14]乙酸酯和[2-C-14]乙酸酯一样。标记的琥珀酸酯在10 mM，而不是1 mM，现在显示出比标记的醋酸酯在这些浓度下的比率更高，因此当与[2-C-14]葡萄糖和[6-C-14]葡萄糖的产率相关时，估计值更高。在配对培养中使用标记的醋酸酯比率，丙酮酸的羧化速率仍然估计为丙酮酸脱羧化速率的三分之二左右。苹果酸酶催化反应的参与解释了在10 mM处琥珀酸产率高于1 mM时(CO2)-C-14的比率，以及葡萄糖加成时这些比率的增加，并解释了在羧化过程中形成的草酰乙酸碳从柠檬酸循环中去除的原因。
Pyruvate has been estimated to enter the citric acid cycle in islets by carboxylation to the same extent or more than by decarboxylation. Those estimates were made assuming the dimethyl esters of [1,4-C-14]succinate and [2-3-C-14]succinate, incubated with islets at a concentration of 10 mM, gave the same ratio of (CO2)-C-14 yields as if [1-C-14]acetate and [2-C-14]acetate had been incubated. The labeled succinates, at 10 mM, but not 1 mM, are now shown to give ratios higher than the labeled acetates at those concentrations and therefore higher estimates when related to yields from [2-C-14]glucose and [6-C-14]glucose. Using the labeled acetate ratios in paired incubations, the rate of pyruvate carboxylation is still estimated to be about two-thirds the rate of pyruvate decarboxylation. Participation of the malic enzyme-catalyzed reaction explains the greater ratio of yields of (CO2)-C-14 from the succinates at 10 mM than 1 mM and increases in those ratios on glucose addition and can account for the removal from the citric acid cycle of oxaloacetate carbon formed in the carboxylation.