Wiskich J T, Bryce J H, Day D A, Dry I B
Departments of Botany, University of Adelaide, Adelaide, South Australia, 5001 Australia.
Plant Physiol. 1990 Jun;93(2):611-6. doi: 10.1104/pp.93.2.611.
The simultaneous oxidation of malate and of glycine was investigated in pea (Pisum sativum) leaf mitochondria. Adding malate to state 4 glycine oxidation did not inhibit, and under some conditions stimulated, glycine oxidation. State 4 oxygen uptake with glycine is restricted because of the control exerted by the membrane potential but reoxidation of NADH by oxaloacetate reduction can still occur. Thus, malate addition stimulates glycine metabolism by producing oxaloacetate. The malate dehydrogenase (EC 1.1.1.37) enzyme fraction remote from glycine decarboxylase (EC 2.1.2.10) oxidizes malate whereas that closely associated with it produces malate, i.e. they function in opposite directions. It is shown that these opposing directions of malate dehydrogenase activity occur within the same mitochondrial matrix compartment and not in different mitochondrial populations. It is concluded that metabolic domains containing different complements of mitochondrial enzymes exist within the one mitochondrial matrix without physical barriers separating them. The differential spatial organization within the matrix may account for the previously reported limited access of some enzymes to the respiratory electron transport chain. The implications for leaf mitochondrial metabolism are discussed.
在豌豆(Pisum sativum)叶片线粒体中研究了苹果酸和甘氨酸的同时氧化。向状态4的甘氨酸氧化体系中添加苹果酸不会抑制甘氨酸氧化,在某些条件下反而会刺激其氧化。由于膜电位的控制,状态4下甘氨酸的氧摄取受到限制,但草酰乙酸还原对NADH的再氧化仍可发生。因此,添加苹果酸通过产生草酰乙酸刺激甘氨酸代谢。远离甘氨酸脱羧酶(EC 2.1.2.10)的苹果酸脱氢酶(EC 1.1.1.37)酶组分氧化苹果酸,而与之紧密相关的酶组分则产生苹果酸,即它们的功能方向相反。结果表明,苹果酸脱氢酶活性的这些相反方向发生在同一个线粒体基质区室中,而不是在不同的线粒体群体中。得出的结论是,在同一个线粒体基质中存在含有不同线粒体酶组合的代谢区域,且没有物理屏障将它们分隔开。基质内的差异空间组织可能解释了先前报道的一些酶对呼吸电子传递链的有限接触。文中讨论了其对叶片线粒体代谢的影响。