Lookup NU author(s): Dr Katsuko Sato,
Professor Christopher Dennison
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The active-site structures of Cu(II) plastocyanins (PCu's) from a higher plant (parsley), a seedless vascular plant (fern, Dryopteris crassirhizoma), a green alga (Ulva pertusa), and cyanobacteria (Anabaena variabilis and Synechococcus) have been investigated by paramagnetic 1H NMR spectroscopy. In all cases the spectra are similar, indicating that the structures of the cupric sites, and the spin density distributions onto the ligands, do not differ greatly between the proteins. The active-site structure of PCu has remained unaltered during the evolutionary process. The electron transfer (et) reactivity of these PCu's is compared utilizing the electron self-exchange (ESE) reaction. At moderate ionic strength (0.10 M) the ESE rate constant is dictated by the distribution of charged amino acid residues on the surface of the PCu's. Most higher plant and the seedless vascular plant PCu's, which have a large number of acidic residues close to the hydrophobic 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 ESE rate constant of ∼104 M-1 s-1. Complete removal of the acidic patch, as in the cyanobacterial PCu's, leads to ESE rate constants of ∼105-106 M-1 s-1. The ESE rate constants of the PCu's with an acidic patch also tend toward ∼105-106 M-1 s-1 at higher ionic strength, thus indicating that once the influence of charged residues has been minimized the et capabilities of the PCu's are comparable. The cytochromes and 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 ESE reactivity has been investigated. When the influence of the acidic patch is minimized, the ESE rate constant decreases at high [H+].
Author(s): Sato K, Kohzuma T, Dennison C
Publication type: Article
Publication status: Published
Journal: Journal of the American Chemical Society
ISSN (print): 0002-7863
ISSN (electronic): 1943-2984
Publisher: American Chemical Society
PubMed id: 12590538
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