NADP-UTILIZING ENZYMES IN THE MATRIX OF PLANT-MITOCHONDRIA
NADP-UTILIZING ENZYMES IN THE MATRIX OF PLANT-MITOCHONDRIA
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DOI：
10.1104/pp.94.3.1012
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发表时间：
1990-11-01
期刊：
影响因子：
7.4
通讯作者：
MOLLER, IM
中科院分区：
文献类型：
--
作者：
RASMUSSON, AG;MOLLER, IM
马铃薯块茎（Solanum tuberosum L.）cv Bintie）线粒体含有可溶的、高度潜伏的NAD+-和NADP+-异柠檬酸脱氢酶、NAD+-和NADP+-苹果酸脱氢酶以及NADPH特异性谷胱甘肽还原酶（分别为160、25、7200、160和16纳摩尔NAD（P）H/分钟和毫克蛋白质）。两种异柠檬酸脱氢酶活性可以用硫酸铵沉淀法分离，但不能分离两种苹果酸脱氢酶活性。因此，NADP+-异柠檬酸脱氢酶活性是由于单独的基质酶，而NADP+-苹果酸脱氢酶活性可能是由于NAD+-苹果酸脱氢酶的非特异性。NADP+特异性异柠檬酸脱氢酶对NADP+和异柠檬酸的Km值（分别为5.1和10.7微摩尔）比NAD+特异性酶（NAD+为101微摩尔，异柠檬酸为184微摩尔）低得多。NADP+特异性异柠檬酸脱氢酶在pH 7.4至9.0的广泛的活性最佳值，而NAD+特异性酶在pH 7.8有一个尖锐的最佳值。在外部NADPH氧化被抑制的条件下，外部添加的NADP+刺激完整线粒体的异柠檬酸和苹果酸氧化。这表明（a）NADP+被线粒体吸收穿过内膜并进入基质，和（B）基质中苹果酸脱氢酶和NADP+特异性异柠檬酸脱氢酶的NADP+还原活性可有助于完整植物线粒体中的电子传递。线粒体NADP（H）和可溶性NADP（H）消耗酶的生理相关性进行了讨论，与其他已知的线粒体NADP（H）利用酶。
Purified potato tuber (Solanum tuberosumL. cv Bintie) mitochondria contain soluble, highly latent NAD+- and NADP+-isocitrate dehydrogenases, NAD+- and NADP+-malate dehydrogenases, as well as an NADPH-specific glutathione reductase (160, 25, 7200, 160, and 16 nanomoles NAD(P)H per minute and milligram protein, respectively). The two isocitrate dehydrogenase activities, but not the two malate dehydrogenase activities, could be separated by ammonium sulfate precipitation. Thus, the NADP+-isocitrate dehydrogenase activity is due to a separate matrix enzyme, whereas the NADP+-malate dehydrogenase activity is probably due to unspecificity of the NAD+-malate dehydrogenase. NADP+-specific isocitrate dehydrogenase had much lowerKms for NADP+and isocitrate (5.1 and 10.7 micromolar, respectively) than the NAD+-specific enzyme (101 micromolar for NAD+and 184 micromolar for isocitrate). A broad activity optimum at pH 7.4 to 9.0 was found for the NADP+-specific isocitrate dehydrogenase whereas the NAD+-specific enzyme had a sharp optimum at pH 7.8. Externally added NADP+stimulated both isocitrate and malate oxidation by intact mitochondria under conditions where external NADPH oxidation was inhibited. This shows that (a) NADP+is taken up by the mitochondria across the inner membrane and into the matrix, and (b) NADP+-reducing activities of malate dehydrogenase and the NADP+-specific isocitrate dehydrogenase in the matrix can contribute to electron transport in intact plant mitochondria. The physiological relevance of mitochondrial NADP(H) and soluble NADP(H)-consuming enzymes is discussed in relation to other known mitochondrial NADP(H)-utilizing enzymes.