Active-Site Structure and Electron-Transfer Reactivity of Plastocyanins
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- 作者：Katsuko Sato ; Takamitsu Kohzuma ; and Christopher Dennison
- 刊名：Journal of the American Chemical Society
- 出版年：2003
- 出版时间：February 26, 2003
- 年：2003
- 卷：125
- 期：8
- 页码：2101 - 2112
- 全文大小：227K
- 年卷期：v.125,no.8(February 26, 2003)
- ISSN：1520-5126
文摘
The active-site structures of Cu(II) plastocyanins (PCu's) from a higher plant (parsley), a seedlessvascular plant (fern, Dryopteris crassirhizoma), a green alga (Ulva pertusa), and cyanobacteria (Anabaenavariabilis and Synechococcus) have been investigated by paramagnetic 1H NMR spectroscopy. In all casesthe spectra are similar, indicating that the structures of the cupric sites, and the spin density distributionsonto the ligands, do not differ greatly between the proteins. The active-site structure of PCu has remainedunaltered during the evolutionary process. The electron transfer (et) reactivity of these PCu's is comparedutilizing the electron self-exchange (ESE) reaction. At moderate ionic strength (0.10 M) the ESE rate constantis dictated by the distribution of charged amino acid residues on the surface of the PCu's. Most higherplant and the seedless vascular plant PCu's, which have a large number of acidic residues close to thehydrophobic patch surrounding the exposed His87 ligand (the proposed recognition patch for the self-exchange process), have ESE rate constants of ~103 M-1 s-1. Removal of some of these acidic residues,as in the parsley and green algal PCu's, results in more favorable protein-protein association and an ESErate constant of ~104 M-1 s-1. Complete removal of the acidic patch, as in the cyanobacterial PCu's, leadsto ESE rate constants of ~105-106 M-1 s-1. The ESE rate constants of the PCu's with an acidic patchalso tend toward ~105-106 M-1 s-1 at higher ionic strength, thus indicating that once the influence ofcharged residues has been minimized the et capabilities of the PCu's are comparable. The cytochromesand Fe-S proteins, two other classes of redox metalloproteins, also possess ESE rate constants of ~105-106 M-1 s-1 at high ionic strength. The effect of the protonation of the His87 ligand in PCu(I) on the ESEreactivity has been investigated. When the influence of the acidic patch is minimized, the ESE rate constantdecreases at high [H+].