Kirchhoff Helmut, Schöttler Mark Aurel, Maurer Julia, Weis Engelbert
Institut für Botanik, Schlossgarten 3, D-48149 Münster, Germany.
Biochim Biophys Acta. 2004 Nov 4;1659(1):63-72. doi: 10.1016/j.bbabio.2004.08.004.
Reduction kinetics of cytochrome f, plastocyanin (PC) and P(700) ('high-potential chain') in thylakoids from spinach were followed after pre-oxidation by a saturating light pulse. We describe a novel approach to follow PC redox kinetics from deconvolution of 810-860 nm absorption changes. The equilibration between the redox-components was analyzed by plotting the redox state of cytochrome f and PC against that of P(700). In thylakoids with (1) diminished electron transport rate (adjusted with a cytochrome bf inhibitor) or (2) de-stacked grana, cytochrome f and PC relaxed close to their thermodynamic equilibriums with P(700). In stacked thylakoids with non-inhibited electron transport, the equilibration plots were complex and non-hyperbolic, suggesting that during fast electron flux, the 'high-potential chain' does not homogeneously equilibrate throughout the membrane. Apparent equilibrium constants <5 were calculated, which are below the thermodynamic equilibrium known for the 'high potential chain'. The disequilibrium found in stacked thylakoids with high electron fluxes is explained by restricted long-range PC diffusion. We develop a model assuming that about 30% of Photosystem I mainly located in grana end-membranes and margins rapidly equilibrate with cytochrome f via short-distance transluminal PC diffusion, while long-range lateral PC migration between grana cores and distant stroma lamellae is restricted. Implications for the electron flux control are discussed.
用饱和光脉冲预氧化后，跟踪菠菜类囊体中细胞色素f、质体蓝素（PC）和P（700）（“高电位链”）的还原动力学。我们描述了一种通过对810 - 860 nm吸收变化进行去卷积来跟踪PC氧化还原动力学的新方法。通过绘制细胞色素f和PC的氧化还原状态与P（700）的氧化还原状态的关系图，分析了氧化还原成分之间的平衡。在（1）电子传输速率降低（用细胞色素bf抑制剂调节）或（2）类囊体垛叠解体的类囊体中，细胞色素f和PC接近它们与P（700）的热力学平衡。在电子传输未受抑制的垛叠类囊体中，平衡图复杂且非双曲线型，这表明在快速电子通量过程中，“高电位链”在整个膜中并非均匀地达到平衡。计算得到的表观平衡常数<5，低于“高电位链”已知的热力学平衡常数。在具有高电子通量的垛叠类囊体中发现的不平衡现象可以通过受限的长距离PC扩散来解释。我们建立了一个模型，假设约30%主要位于类囊体垛叠末端膜和边缘的光系统I通过短距离的跨腔PC扩散与细胞色素f迅速达到平衡，而类囊体垛叠核心与远处基质片层之间的长距离横向PC迁移受到限制。讨论了其对电子通量控制的影响。
