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Effect of pH on the self-exchange reactivity of the plant plastocyanin from parsley

Lookup NU author(s): Dr David Hunter, Emeritus Professor William McFarlane, Emeritus Prof Alfred Sykes, Professor Christopher Dennison


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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 patch in 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% of the reduced protein molecules (pKa* 5.6), and this would be expected to hinder electron transfer between the two oxidation states. However, this effect is counterbalanced by the enhanced association of two parsley plastocyanins at lower pH* due to the partial protonation of the acidic patch.

Publication metadata

Author(s): Hunter DM; Sykes AG; Dennison C; McFarlane W

Publication type: Article

Publication status: Published

Journal: Inorganic Chemistry

Year: 2001

Volume: 40

Issue: 2

Pages: 354-360

ISSN (print): 0020-1669

ISSN (electronic): 1520-510X

Publisher: American Chemical Society


DOI: 10.1021/ic000798n

PubMed id: 11170543


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