Day D A, Neuburger M, Douce R
Arch Biochem Biophys. 1984 May 15;231(1):233-42. doi: 10.1016/0003-9861(84)90383-7.
O2 uptake by potato and cauliflower bud mitochondria oxidizing malate was progressively inhibited as the pH of the external medium was increased, in response to accumulation of oxaloacetate. Adding 0.5 mM coenzyme A to the medium reversed this trend by stimulating intramitochondrial NAD-linked malic enzyme at alkaline pH. In intact potato mitochondria, coenzyme A stimulation of malic enzyme was not observed when the external pH was above 7.5; in cauliflower mitochondria, coenzyme A stimulated even at pH 8. This difference in the response of intact mitochondria was attributed to an inherent difference in the properties of malic enzyme from the two tissues. Malic enzyme solubilized from potato mitochondria was inactive at pH values above 7.8, while that from cauliflower mitochondria retained its activity at pH 8 in the presence of coenzyme A. In potato mitochondria, coenzyme A stimulation of O2 uptake at alkaline pH was only observed when NAD+ was also provided exogenously. The results show that coenzyme A can be taken up by intact mitochondria and that pH, NAD+, and coenzyme A levels in the matrix act together to regulate malate oxidation.
随着外部介质pH值的升高，由于草酰乙酸的积累，马铃薯和花椰菜芽线粒体氧化苹果酸时的氧气摄取逐渐受到抑制。向介质中添加0.5 mM辅酶A可通过在碱性pH值下刺激线粒体内NAD连接的苹果酸酶来逆转这一趋势。在完整的马铃薯线粒体中，当外部pH值高于7.5时，未观察到辅酶A对苹果酸酶的刺激作用；在花椰菜线粒体中，即使在pH 8时辅酶A也能起到刺激作用。完整线粒体反应的这种差异归因于两种组织中苹果酸酶性质的固有差异。从马铃薯线粒体中溶解的苹果酸酶在pH值高于7.8时无活性，而从花椰菜线粒体中溶解的苹果酸酶在有辅酶A存在的情况下在pH 8时仍保持其活性。在马铃薯线粒体中，只有在外源提供NAD+时，才观察到碱性pH值下辅酶A对氧气摄取的刺激作用。结果表明，完整的线粒体可以摄取辅酶A，并且基质中的pH值、NAD+和辅酶A水平共同作用来调节苹果酸氧化。
