Kaminskaya O, Kurreck J, Irrgang K D, Renger G, Shuvalov V A
Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino, Moscow Region.
Biochemistry. 1999 Dec 7;38(49):16223-35. doi: 10.1021/bi991257g.
A detailed analysis of the properties of cytochrome b(559) (Cyt b(559)) in photosystem II (PS II) preparations with different degrees of structural complexity is presented. It reveals that (i) D1-D2-Cyt b(559) complexes either in solubilized form or incorporated into liposomes contain only one type of Cyt b(559) with E(m) values of 60 +/- 5 and 100 +/- 10 mV, respectively, at pH 6.8; (ii) in oxygen-evolving solubilized PS II core complexes Cyt b(559) exists predominantly (>85%) as an LP form with an E(m,7) of 125 +/- 10 mV and a minor fraction with an E(m,7) of -150 +/- 15 mV; (iii) in oxygen-evolving PS II membrane fragments three different redox forms are discernible with E(m) values of 390 +/- 15 mV (HP form), 230 +/- 20 mV (IP form), and 105 +/- 25 mV (LP form) and relative amplitudes of 58, 24, and 18%, respectively, at pH 7.3; (iv) the E(m) values are almost pH-independent between pH 6 and 9.5 in all sample types except D1-D2-Cyt b(559) complexes incorporated into liposomes with a slope of -29 mV/pH unit, when the pH increases from 6 to 9.5 (IP and LP form in PS II membrane fragments possibly within a restricted range from pH 6.5 to 8); (v) at pH >8 the HP Cyt b(559) progressively converts to the IP form with increasing pH; (vi) the reduced-minus-oxidized optical difference spectra of Cyt b(559) are very similar in the lambda range of 360-700 nm for all types except for the HP form which exhibits pronounced differences in the Soret band; and (vii) PS II membrane fragments and core complexes are inferred to contain about two Cyt b(559) hemes per PS II. Possible implications of conformational changes near the heme group and spin state transitions of the iron are discussed.
本文对具有不同结构复杂程度的光系统II（PS II）制剂中细胞色素b(559)（Cyt b(559)）的性质进行了详细分析。结果表明：（i）以溶解形式或整合到脂质体中的D1-D2-Cyt b(559)复合物仅含有一种类型的Cyt b(559)，在pH 6.8时，其E(m)值分别为60±5和100±10 mV；（ii）在放氧的溶解PS II核心复合物中，Cyt b(559)主要以LP形式存在（>85%），E(m,7)为125±10 mV，一小部分E(m,7)为-150±15 mV；（iii）在放氧的PS II膜片段中，可分辨出三种不同的氧化还原形式，在pH 7.3时，E(m)值分别为390±15 mV（HP形式）、230±20 mV（IP形式）和105±25 mV（LP形式），相对幅度分别为58%、24%和18%；（iv）除了整合到脂质体中的D1-D2-Cyt b(559)复合物外，所有样品类型在pH 6至9.5之间，E(m)值几乎与pH无关，当pH从6增加到9.5时，其斜率为-29 mV/pH单位（PS II膜片段中的IP和LP形式可能在pH 6.5至8的受限范围内）；（v）在pH>8时，HP Cyt b(559)随着pH升高逐渐转化为IP形式；（vi）除HP形式在Soret带表现出明显差异外，所有类型的Cyt b(559)在360-700 nm波长范围内的还原态减去氧化态光学差光谱非常相似；（vii）推断PS II膜片段和核心复合物每个PS II含有约两个Cyt b(559)血红素。讨论了血红素基团附近构象变化和铁的自旋态转变的可能影响。
