Unusual low reactivity of the water oxidase in redox state S3 toward exogenous reductants. Analysis of the NH2OH- and NH2NH2-induced modifications of flash-induced oxygen evolution in isolated spinach thylakoids.
Unusual low reactivity of the water oxidase in redox state S3 toward exogenous reductants. Analysis of the NH2OH- and NH2NH2-induced modifications of flash-induced oxygen evolution in isolated spinach thylakoids.
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氧化还原态 S3 的水氧化酶对外源还原剂的反应性异常低。
DOI：
10.1021/bi00245a027
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发表时间：
1991
期刊：
影响因子：
2.9
通讯作者：
G. Renger
中科院分区：
文献类型：
--
作者：
J. Messinger;U. Wacker;G. Renger
在离体菠菜类囊体中分析了氧化还原活性胺NH_2 R（R = OH或NH_2）作为氧化还原态Si（i = 0，...，3)水氧化酶。结果表明：（a）在暗适应的样品中，NH_2 R通过暗反应序列形成S-1态，（B）NH_2 R的反应机理不同; NH 2 OH充当单电子供体，而NH 2NH 2主要充当双电子供体，与相互作用的氧化还原态Si（i = 0，.，3）。对于NH_2NH_2，修正的氧振荡模式严格依赖于加入还原剂前的初始比值[S_0（0）]/[S_1（0）];而对于NH_2OH，由于动力学原因，这种依赖性在短暂的过渡期后基本消失。(c)最近假定的形式氧化还原态“S-2”的存在不仅在NH 2NH 2的存在下得到证实[Renger，G.，Messinger，J.，& Hanssum，B.（1990）在Current Research in Photosynthesis（Baltscheffsky，M.，编辑）第1卷，第845-848页，Kluwer，多尔德雷赫特]，而且在NH 2 OH存在下进行。(d)活化能，EA，50千焦/摩尔的测定为NH 2 R诱导的还原过程，改变了氧振荡模式从黑暗适应类囊体。(e)虽然NH_2OH和NH_2NH_2在还原机理和还原效率方面存在显著差异，（这是有利于NH 2 OH的约20倍），两种NH 2 R物质表现出相同数量级的速率常数作为未扰动水氧化酶中氧化还原态Si的函数：kNH 2 R（S 0）大于kNH 2 R（S1）远小于kNH 2 R（S2）远大于kNH 2 R（S3）S_2和S_3对NH_2R的反应性的巨大差异被解释为表明电子构型和核构型的显著变化。在S2----S3转变期间发生的几何结构使得S3状态对NH 2 R的敏感性小得多。这些发现的含义进行了讨论，特别强调了在氧化还原状态S3中形成络合过氧化物的可能性，该氧化还原状态S3是先前基于理论考虑而假设的[Renger，G.（1978）在光合水氧化（Metzner，H.，编辑）第229-248页，学术出版社，伦敦]。
The effect of redox-active amines NH2R (R = OH or NH2) on the period-four oscillation pattern of oxygen evolution has been analyzed in isolated spinach thylakoids as a function of the redox state Si (i = 0, ..., 3) of the water oxidase. The following results were obtained: (a) In dark-adapted samples with a highly populated S1 state, NH2R leads via a dark reaction sequence to the formal redox state "S-1"; (b) the reaction mechanism is different between the NH2R species; NH2OH acts as a one-electron donor, whereas NH2NH2 mainly functions as a two-electron donor, regardless of the interacting redox state Si (i = 0, ..., 3). For NH2NH2, the modified oxygen oscillation patterns strictly depend upon the initial ratio [S0(0)]/[S1(0)] before the addition of the reductant; while due to kinetic reasons, for NH2OH this dependence largely disappears after a short transient period. (c) The existence of the recently postulated formal redox state "S-2" is confirmed not only in the presence of NH2NH2 [Renger, G., Messinger, J., & Hanssum, B. (1990) in Current Research in Photosynthesis (Baltscheffsky, M., Ed.) Vol. 1, pp 845-848, Kluwer, Dordrecht] but also in the presence of NH2OH. (d) Activation energies, EA, of 50 kJ/mol were determined for the NH2R-induced reduction processes that alter the oxygen oscillation pattern from dark-adapted thylakoids. (e) Although marked differences exist between NH2OH and NH2NH2 in terms of the reduction mechanism and efficiency (which is about 20-fold in favor of NH2OH), both NH2R species exhibit the same order of rate constants as a function of the redox state Si in the nonperturbed water oxidase: kNH2R(S0) greater than kNH2R(S1) much less than kNH2R(S2) much greater than kNH2R(S3) The large difference between S2 and S3 in their reactivity toward NH2R is interpreted to indicate that a significant change in the electronic configuration and nuclear geometry occurs during the S2----S3 transition that makes the S3 state much less susceptible to NH2R. The implications of these findings are discussed with special emphasis on the possibility of complexed peroxide formation in redox state S3 postulated previously on the basis of theoretical considerations [Renger, G. (1978) in Photosynthetic Water Oxidation (Metzner, H., Ed.) pp 229-248, Academic Press, London].