Evans R M, Scholz R W
Biochim Biophys Acta. 1975 Feb 13;381(2):278-91. doi: 10.1016/0304-4165(75)90234-2.
Rat lung mitochondrial preparations were incubated in the preasence of pyruvate and malate. The principal metabolic products measured were citrate and CO2. Citrate formation from pyruvate was found to be dependent on the presence of malate. Significant citrate was formed in the presence of isocitrate and the rate of citrate formation was increased by the addition of pyruvate. Small amounts of citrate were formed by lung mitochondrial preparations in the presence of 2-oxoglutarate and succinate only after the addition of pyruvate. The level of acetyl-CoA was significantly greater in the presence of pyruvate than in the presence of pyruvate plus malate. The addition of malate to lung mitoochondrial preparations increased 14CO2 production from [2-14C] pyruvate into malate and citrate. A low level of pyruvate-dependent H14CO3-incorporation into acid-stable products was observed, principally citrate and malate, but this rate did not exceed 5% of the rate of net citrate formation in the presence of malate and pyruvate. The capacity of rate lung mitochondria to form oxaloacetate from pyruvate alone in vitro is very limited, and would appear to cast doubt on a major role of pyruvate carboxylase in citrate formation. It is concluded that the rate of citrate formation from pyruvate is limited by the availability of intramitochondrial oxaloacetate and the rate of citrate efflux across the mitochondrial membrane.
大鼠肺线粒体制剂在丙酮酸和苹果酸存在的情况下进行孵育。所测定的主要代谢产物是柠檬酸和二氧化碳。发现由丙酮酸生成柠檬酸依赖于苹果酸的存在。在异柠檬酸存在的情况下会生成大量柠檬酸，并且添加丙酮酸会提高柠檬酸的生成速率。仅在添加丙酮酸后，肺线粒体制剂在2-氧代戊二酸和琥珀酸存在的情况下才会生成少量柠檬酸。丙酮酸存在时乙酰辅酶A的水平显著高于丙酮酸加苹果酸存在时的水平。向肺线粒体制剂中添加苹果酸会增加[2-¹⁴C]丙酮酸生成苹果酸和柠檬酸过程中¹⁴CO₂的产生量。观察到丙酮酸依赖性的低水平¹⁴HCO₃掺入酸稳定产物中，主要是柠檬酸和苹果酸，但该速率不超过苹果酸和丙酮酸存在时柠檬酸净生成速率的5%。离体状态下，肺线粒体仅由丙酮酸生成草酰乙酸的能力非常有限，这似乎对丙酮酸羧化酶在柠檬酸生成中的主要作用提出了质疑。得出的结论是，丙酮酸生成柠檬酸的速率受线粒体内草酰乙酸的可用性以及柠檬酸跨线粒体膜流出速率的限制。
