Rates and properties of endogenous cyclic photophosphorylation of isolated intact chloroplasts measured by CO2 fixation in the presence of dihydroxyacetone phosphate.
Rates and properties of endogenous cyclic photophosphorylation of isolated intact chloroplasts measured by CO2 fixation in the presence of dihydroxyacetone phosphate.
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在磷酸二羟丙酮存在下，通过 CO2 固定测量分离的完整叶绿体的内源循环光磷酸化的速率和特性。
DOI：
10.1016/0005-2728(76)90103-1
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发表时间：
1976
期刊：
影响因子：
--
通讯作者：
W. Urbach
中科院分区：
文献类型：
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作者：
W. Kaiser;W. Urbach
1.二羟基丙酮磷酸在浓度为2.5 mM完全抑制CO2依赖的O2进化分离完整的菠菜叶绿体。这种抑制作用通过加入等摩尔浓度的Pi而逆转，但不通过加入3-磷酸甘油酸而逆转。在不存在Pi、3-磷酸甘油酸和磷酸二羟丙酮的情况下，在上清液中仅发现约20%的14 C-标记的中间体，而在存在这些物质中的每一种的情况下，上清液中标记的中间体的百分比增加到70- 95%。在此基础上，结合完整叶绿体被膜中已知的磷酸转运蛋白的功能，对磷酸二羟丙酮抑制放氧的机制进行了讨论.虽然O2的释放被磷酸二羟丙酮完全抑制，但CO2的固定在空气中发生，速率高达65μ mol · mg− 1叶绿素· h−1。由于在这些条件下显然不发生非循环电子传递，因此这些速率一定是由于内源性假环状和/或环状磷酸化。在厌氧条件下，磷酸二羟丙酮存在下的CO2固定速率很低（2.5-7 μmol · mg− 1叶绿素· h−1），但加入二氯苯基二甲基脲（例如2 · 10− 7 M）可强烈刺激CO2固定速率，达到60 μmol · mg− 1叶绿素· h−1。由于在此条件下，CO2固定所需的ATP可以通过内源性环状磷酸化形成，因此该过程的能力似乎相对较高，因此它可能对叶绿体的能量供应有重要贡献。由于二氯苯基二甲基脲刺激CO2固定在磷酸二羟丙酮存在下，在厌氧条件下，但不是在有氧条件下，它的结论是，只有在厌氧条件下的“过度还原”的循环电子传递系统发生，这是除去二氯苯基二甲基脲在适当的浓度。当浓度高于5 · 10− 7 M时，二氯苯二甲基脲会抑制厌氧和有氧条件下依赖磷酸二羟丙酮的CO2固定，其方式与正常的CO2固定类似。因此，我们假设电子传递链的适当平衡的氧化还原状态对于内源性环状磷酸化的最佳发生是必要的。二溴百里醌在厌氧条件下抑制二氯苯二甲基脲刺激的CO2固定在磷酸二羟丙酮的存在下，表明质体醌是一个不可缺少的组成部分的内源性循环电子途径。
1. Dihydroxyacetone phosphate in concentrations ⩾ 2.5 mM completely inhibits CO2-dependent O2evolution in isolated intact spinach chloroplasts. This inhibition is reversed by the addition of equimolar concentrations of Pi, but not by addition of 3-phosphoglycerate. In the absence of Pi, 3-phosphoglycerate and dihydroxyacetone phosphate, only about 20% of the14C-labelled intermediates are found in the supernatant, whereas in the presence of each of these substances the percentage of labelled intermediates in the supernatant is increased up to 70–95%. Based on these results the mechanism of the inhibition of O2evolution by dihydroxyacetone phosphate is discussed with respect to the function of the known phosphate translocator in the envelope of intact chloroplasts.2. Although O2evolution is completely suppressed by dihydroxyacetone phosphate, CO2fixation takes place in air with rates of up to 65μ mol · mg−1chlorophyll · h−1. As non-cyclic electron transport apparently does not occur under these conditions, these rates must be due to endogenous pseudocyclic and/or cyclic photophosphorylation.3. Under anaerobic conditions, the rates of CO2fixation in presence of dihydroxyacetone phosphate are low (2.5–7 μmol · mg−1chlorophyll · h−1), but they are strongly stimulated by addition of dichlorophenyl-dimethylurea (e.g. 2 · 10−7M) reaching values of up to 60 μmol · mg−1chlorophyll · h−1. As under these conditions the ATP necessary for CO2fixation can be formed by an endogenous cyclic photophosphorylation, the capacity of this process seems to be relatively high, so it might contribute significantly to the energy supply of the chloroplast. As dichlorophenyl-dimethylurea stimulates CO2fixation in presence of dihydroxyacetone phosphate under anaerobic but not under aerobic conditions, it is concluded that only under anaerobic conditions an “overreduction” of the cyclic electron transport system takes place, which is removed by dichlorophenyl-dimethylurea in suitable concentrations. At concentrations above 5 · 10−7M dichlorophenyl-dimethylurea inhibits dihydroxyacetone phosphate-dependent CO2fixation under anaerobic as well as under aerobic conditions in a similar way as normal CO2fixation. Therefore, we assume that a properly poised redox state of the electron transport chain is necessary for an optimal occurrence of endogenous cyclic photophosphorylation.4. The inhibition of dichlorophenyl-dimethylurea-stimulated CO2fixation in presence of dihydroxyacetone phosphate by dibromothymoquinone under anaerobic conditions indicates that plastoquinone is an indispensible component of the endogenous cyclic electron pathway.