教育专题：叶绿体能利用外源ATP吗？

叶绿体能利用外源ATP吗？转自汉水群木可老师的博客叶绿体能利用外源ATP吗？关于这个问题，部分老师的回答是“否”的，理由是产生ATP的光反应阶段使叶绿体在ATP的利用上完全“自给自足”叶绿体既不会为之外的其它生理活动提供ATP，也不会吸收利用由细胞呼吸产生的外源性ATP。事实上，光反应产生的ATP确实仅用于叶绿体自身的合成代谢，但叶绿体完全可以从细胞溶胶中吸收少部分来自细胞呼吸的ATP，以满足特定条件下叶绿体中的代谢需求，如碳反应、DNA的复制、蛋白质的合成等，实现这一点的分子基础就是位于叶绿体内膜上的ATP/ADP交换转运体。以下是本人参考的国外论文中的关键文字，翻译水平有限，不正确的地方请大家指正。引自：Herbert H.Winkler and H.Ekkehard Neuhaus.1999. Non-mitochondrial ATP transport. Elsevier Science,66.原文： It is generally assumed that the ATP required for photosynthetic CO2 fixation derives from the ATP synthase driven by the pH gradient across the thylakoid membrane. However, there are several indications that, at least under certain conditions or in certain types of chloroplast, the uptake of cytosolic ATP supplements anabolic reactions. Such an ATP uptake would be required when photosynthesis does not deliver sufficient ATP for CO2 fixation and other anabolic reactions. The plastidic ATP/ADP transporter should be responsible for translocating ATP generated in the mitochondria from cytosol to stroma in these circumstances(see Fig. 3). Depending on the rate of ATP uptake, the transport of ATP might contribute to carbon fixation either by only a few percent or substantially. Import of ATP ranges from 5 micromoles per milligram of chlorophyll per hour (in spinach chloroplasts) 5 to 40 micromoles per milligram of chlorophyll per hour (in Digitaria sanguinalis chloroplasts)29. Finally, in isolated chloroplasts from sweet-pepper fruits, the addition of ATP results in the highest observed rates of starch biosynthesis in the light 30. In conclusion, photosynthetic carbon metabolism in several organisms is obviously positively influenced by exogenous ATP; the plastidic ATP/ADP transporter is thus important in both heterotrophic plastids (i.e. amyloplasts) and photoautotrophic plastids (i.e. chloroplasts).翻译： 通常认为光合作用CO2固定所需的ATP来自于由类囊体膜两侧PH梯度驱动的ATP合成过程，然而，一些证据表明，从细胞溶胶中吸收ATP可补充叶绿体的合成代谢，这至少在某些条件下或者某些类型的叶绿体中是如此。当光合作用不能为CO2固定或其它合成代谢提供足量的ATP时，叶绿体就需要吸收ATP。质体的ATP/ADP转运体负责将线粒体产生的ATP从细胞溶胶转运到质体基质中。（见图3）ATP运输可能对光合作用的碳固定产生很少的或实质性的促进作用，程度视ATP的吸收速度而定。在实验中，ATP的输入范围从每小时每毫克叶绿素5 微摩尔(波菜叶绿体)到每小时每毫克叶绿素40 微摩尔(马唐草叶绿体)。在光下，给甜辣椒的离体叶绿体加入ATP后，淀粉的表观合成速率达到了最大值。总之，一些生物的光合作用碳反应受到外源性ATP的显著影响；质体ATP/ADP转运体在异养型质体（如造粉体）和光能自养型质体（如叶绿体）中都具有重要的作用。