光系统I中反应中心叶绿素（P700）的氧化还原电位。低温下电子顺磁共振信号1中多组分的证据。

The oxidation-reduction potential of the reaction-centre chlorophyll (P700) in Photosystem I. Evidence for multiple components in electron-paramagnetic-resonance signal 1 at low temperature.

作者信息

Evans M C, Sihra C K, Slabas A R

出版信息

Biochem J. 1977 Jan 15;162(1):75-85. doi: 10.1042/bj1620075.

DOI:10.1042/bj1620075

PMID:192214

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC1164571/

Abstract

The oxidation-reduction potential of the reaction-centre chlorophyll of Photosystem I (P700) in spinach chloroplasts was determined by using the ability of the reaction centre to photoreduce the bound ferredoxin and to photo-oxidize P700 on illumination at 20K as an indicator of the oxidation state of P700. This procedure shows that P700 is oxidized with Em (pH8.0)(mid-point redox potential at pH8.0)congruent to +375mV. Further oxidation of the chloroplast preparations by high concentrations of K3Fe(CN)6(10mM) in the presence of mediating dyes leads to the appearance of a large radical signal with an apparent Em congruent to +470mVA second, light-inducible, radical also appears over the same potential range. We propose that these signals are due to bulk chlorophyll oxidation and not, as was previously thought [Knaff & Malkin (1973) Arch. Biochem. Biophys. 159, 555-562], to reaction-centre oxidation. A number of optical techniques were used to determine Em of P700. Dual-wavelength spectroscopy (697-720nm) indicates Em congruent to +460-+480mV. The spectrum of the sample during the titration showed a large contribution to the signal by bulk chlorophyll oxidation, in agreement with the electron-paramagnetic-resonance results and those of Ke, Sugahara & Shaw [(1975) Biochim. Biophys. Acta 408, 12-25]. The light-induced absorbance change at 435 nm, usually attributed to P700, showed a potential dependence similar to that of bulk chlorophyll oxidation. Determination of Em of P700 on the basis of the appearance of the P700 signal in oxidized-versus-reduced difference spectra showed Em (pH8.0) congruent to +360mV. Measurements of the effect of potential on the irreversible photo-oxidation of P700 at 77K showed that P700 became oxidized in this potential range. We conclude that the reaction-centre chlorophyll of Photosystem I has Em (pH8.0) congruent to +375mV.

摘要

通过利用反应中心在20K光照下光还原结合态铁氧化还原蛋白以及光氧化P700的能力作为P700氧化态的指标，测定了菠菜叶绿体中光系统I（P700）反应中心叶绿素的氧化还原电位。该方法表明，P700被氧化时，其Em（pH8.0）（pH8.0时的中点氧化还原电位）约为+375mV。在存在介导染料的情况下，用高浓度的K3Fe(CN)6（10mM）进一步氧化叶绿体制剂，会导致出现一个大的自由基信号，其表观Em约为+470mV。其次，在相同电位范围内还会出现一个光诱导的自由基。我们认为这些信号是由于大量叶绿素氧化所致，而不是像之前所认为的那样[克纳夫和马尔金（1973年）《生物化学与生物物理学报》159卷，555 - 562页]，是由于反应中心氧化。使用了多种光学技术来测定P700的Em。双波长光谱法（697 - 720nm）表明Em约为+460 - +480mV。滴定过程中样品的光谱显示大量叶绿素氧化对信号有很大贡献，这与电子顺磁共振结果以及Ke、杉原和肖[（1975年）《生物化学与生物物理学报》408卷，12 - 25页]的结果一致。通常归因于P700的435nm处的光诱导吸光度变化显示出与大量叶绿素氧化相似的电位依赖性。根据氧化态与还原态差光谱中P700信号的出现来测定P700的Em，结果显示Em（pH8.0）约为+360mV。在77K下测量电位对P700不可逆光氧化的影响表明，P700在该电位范围内被氧化。我们得出结论，光系统I的反应中心叶绿素的Em（pH8.0）约为+375mV。