Effect of pH on the Self-Exchange Reactivity of the Plant Plastocyanin from Parsley

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• 作者：David M. Hunter ; William McFarlane ; A. Geoffrey Sykes ; and Christopher Dennison
• 刊名：Inorganic Chemistry
• 出版年：2001
• 出版时间：January 15, 2001
• 年：2001
• 卷：40
• 期：2
• 页码：354 - 360
• 全文大小：104K
• 年卷期：v.40,no.2(January 15, 2001)
• ISSN：1520-510X

文摘

The self-exchange rate constant (25 C) for parsley plastocyanin is 5.0 × 10⁴ M^-1 s^-1 at pH* 7.5 (I = 0.10 M).This value is quite large for a higher plant plastocyanin and can be attributed to a diminished upper acidic patchin this protein. The self-exchange rate constant is almost independent of pH* in the range 7.5-5.6, with a value(25 C) of 5.6 × 10⁴ M^-1 s^-1 at pH* 5.6 (I = 0.10 M). At this pH*, the ligand His87 is protonated in ~50% ofthe reduced protein molecules (pK_a* 5.6), and this would be expected to hinder electron transfer between the twooxidation states. However, this effect is counterbalanced by the enhanced association of two parsley plastocyaninsat lower pH* due to the partial protonation of the acidic patch.