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首页> 外文期刊>Biochimica et biophysica acta: international journal of biochemistry and biophysics >Photosystem II of peas: effects of added divalent cations of Mn, Fe, Mg, and Ca on two kinetic components of P(+)(680) reduction in Mn-depleted core particles.
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Photosystem II of peas: effects of added divalent cations of Mn, Fe, Mg, and Ca on two kinetic components of P(+)(680) reduction in Mn-depleted core particles.

机译：豌豆的光系统II：锰，铁，镁和钙的二价阳离子添加对贫锰芯颗粒中P（+）（680）还原的两个动力学成分的影响。

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摘要

The catalytic Mn cluster of the photosynthetic oxygen-evolving system is oxidized via a tyrosine, Y(Z), by a photooxidized chlorophyll a moiety, P(+)(680). The rapid reduction of P(+)(680) by Y(Z) in nanoseconds requires the intactness of an acid/base cluster around Y(Z) with an apparent functional pK of <5. The removal of Mn (together with bound Ca) shifts the pK of the acid/base cluster from the acid into the neutral pH range. At alkaline pH the electron transfer (ET) from Y(Z) to P(+)(680) is still rapid (<1 micros), whereas at acid pH the ET is much slower (10-100 micros) and steered by proton release. In the intermediate pH domain one observes a mix of these kinetic components (see R. Ahlbrink, M. Haumann, D. Cherepanov, O. Bogershausen, A. Mulkidjanian, W. Junge, Biochemistry 37 (1998)). The overall kinetics of P(680)(+) reduction by Y(Z) in Mn-depleted photosystem II (PS II) has been previously shown to be slowed down by divalent cations (added at >10 microM), namely: Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+) (C.W. Hoganson, P.A. Casey, O. Hansson, Biochim. Biophys. Acta 1057 (1991)). Using Mn-depleted PS II core particles from pea as starting material, we re-investigated this phenomenon at nanosecond resolution, aiming at the effect of divalent cations on the particular kinetic components of P(+)(680) reduction. To our surprise we found only the slower, proton steered component retarded by some added cations (namely Co(2+)/Zn(2+)>Fe(2+)>Mn(2+)). Neither the fast component nor the apparent pK of the acid/base cluster around Y(Z) was affected. Apparently, the divalent cations acted (electrostatically) on the proton release channel that connects the oxygen-evolving complex with the bulk water, but not on the ET between Y(Z) and P(+)(680), proper. Contrastingly, Ca(2+) and Mg(2+), when added at >5 mM, accelerated the slow component of P(+)(680) reduction by Y(Z) and shifted the apparent pK of Y(Z) from 7.4 to 6.6 and 6.7, respectively. It was evident that the binding site(s) for added Ca(2+) and Mg(2+) were close to Y(Z) proper. The data obtained are discussed in relation to the nature of the metal-binding sites in photosystem II.
机译：通过光氧化的叶绿素a部分P（+）（680）经由酪氨酸Y（Z）氧化光合作用的氧气演化系统的Mn簇。 Y（Z）在几纳秒内将P（+）（680）快速还原需要完整的Y / Z周围的酸/碱簇，表观功能性pK <5。 Mn（与结合的Ca一起）的去除将酸/碱簇的pK从酸转移到中性pH范围内。在碱性pH值下，从Y（Z）到P（+）（680）的电子转移（ET）仍然很迅速（<1 micros），而在酸性pH值下，ET则要慢得多（10-100 micros），并且受质子控制发布。在中间pH域中，人们观察到了这些动力学成分的混合（参见R.Ahlbrink，M.Haumann，D.Cherepanov，O.Bogershausen，A.Mulkidjanian，W.Junge，生物化学37（1998））。先前已显示，二价阳离子（以> 10 microM的量添加）会减缓Mn耗尽的光系统II（PS II）中Y（Z）还原P（680）（+）的整体动力学，即：Mn（ 2 +），Co（2 +），Ni（2 +），Cu（2 +），Zn（2+）（CW Hoganson，PA Casey，O.Hansson，Biochim.Biophys.Acta 1057（1991））。以豌豆中贫锰的PS II核心颗粒为起始材料，我们以纳秒分辨率重新研究了该现象，旨在研究二价阳离子对P（+）（680）还原的特定动力学成分的影响。令我们惊讶的是，我们发现只有较慢的质子操纵成分受某些添加阳离子（即Co（2 +）/ Zn（2 +）> Fe（2 +）> Mn（2+））的阻滞。 Y（Z）附近的酸/碱簇的快速组分或表观pK均不受影响。显然，二价阳离子（静电地）作用在质子释放通道上，质子释放通道将放氧复合物与大量水相连，但不作用在Y（Z）和P（+）（680）之间的ET上。相反，当Ca（2+）和Mg（2+）添加> 5 mM时，P（+）（680）还原的缓慢成分加速了Y（Z），并使Y（Z）的表观pK从分别为7.4至6.6和6.7。显然，添加的Ca（2+）和Mg（2+）的结合位点接近Y（Z）合适的结合位点。讨论了有关光系统II中金属结合位点性质的数据。

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