Williams-Smith D L, Heathcote P, Sihra C K, Evans M C
Biochem J. 1978 Feb 15;170(2):365-71. doi: 10.1042/bj1700365.
E.p.r. spectrometry was used to investigate the quantitative relationships between the oxidized chlorophyll free-radical signal I and the reduced iron-sulphur centre-A signal generated on illuminating Photosystem-I particles at cryogenic temperatures. In Photosystem-I particles prepared by using the French press or Triton X-100, at pH8.0 in the presence and absence of ascorbate and at pH 10.0 in the presence of ascorbate, the size of the light-induced signal I and iron-sulphur centre-A signals, corresponded to equal numbers of unpaired electron spins in each component. At 77K the spin-lattice relaxation time, T1, of the free radical signal I in samples of Photosystem-I particles prepared with Triton X-100 in the absence of ascorbate was 0.68 times the T1 value in the presence of ascorbate. Such changes in relaxation time can account for the different quantitative conclusions incorrectly arrived at from measurements made at saturating microwave powers [Bearden & Malkin (1976) Biochem. Biophys. Acta 430, 538-547; Malkin & Bearden (1976) FEBS Lett. 69, 216-220]. In the presence of benzoquinone and ferricyanide the ratio of free radical to centre A was 2.96:1, and at 77K the T1 was 0.50 times the T1 for ascorbate-treated samples. Here free radicals from bulk chlorophyll are generated in addition to those from the reaction-centre chlorophyll.
电子顺磁共振光谱法被用于研究在低温下照射光系统I颗粒时产生的氧化叶绿素自由基信号I与还原型铁硫中心A信号之间的定量关系。在用法国压榨机或曲拉通X - 100制备的光系统I颗粒中，在pH8.0、有无抗坏血酸存在的情况下以及在pH10.0且有抗坏血酸存在的情况下，光诱导信号I和铁硫中心A信号的大小对应于每个组分中相等数量的未成对电子自旋。在77K时，在没有抗坏血酸的情况下用曲拉通X - 100制备的光系统I颗粒样品中，自由基信号I的自旋晶格弛豫时间T1是有抗坏血酸存在时T1值的0.68倍。弛豫时间的这种变化可以解释从在饱和微波功率下进行的测量中错误得出的不同定量结论[比尔登和马尔金（1976年）《生物化学与生物物理学报》430卷，第538 - 547页；马尔金和比尔登（1976年）《欧洲生物化学学会联合会快报》69卷，第216 - 220页]。在存在苯醌和铁氰化物的情况下，自由基与中心A的比例为2.96:1，并且在77K时，T1是抗坏血酸处理样品T1的0.50倍。除了来自反应中心叶绿素的自由基外，还会产生来自大量叶绿素的自由基。
