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The effect of water on the Fe3+/Fe2+ reduction potential of heme
Kungliga tekniska högskolan, KTH.
Rice University, Houston.
University of Hongkong.
Umeå universitet.
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2000 (English)In: Biochemical and Biophysical Research Communications - BBRC, ISSN 0006-291X, E-ISSN 1090-2104, Vol. 268, no 3, p. 683-687Article in journal (Refereed) Published
Abstract [en]

Hemeproteins can act as catalysts, oxygen carriers or electron conductors. The ferric/ferrous reduction potential Em7 of iron in the center of the prosthetic group ranges from negative values for peroxidases to an extreme positive value for cytochrome a3 with Hb and Mb in the middle [1]. Proteins exercise their influence on Em7 in several ways: via substituents at the periphery of the chelate structure, via the proximal ligand, and via interaction with the surrounding medium, amino acid side chains, or polar solvents. Work on recombined proteins and 2,4-substituted free hemes documented that the first two effects are additive [2]. For the third effect, models of the dielectric media on a molecular level have been successfully applied [3-5]. Em7 has also been empirically correlated to the degree of heme exposure to water [6-8]. The apoprotein/porphyrin and water/porphyrin interfaces are complementary since water molecules fill any empty space in the crevice and surround any pertinent part of heme outside the protein boundary. The present work links to this idea by a combination of statistical mechanics simulations and quantum mechanical calculations comparing heme in water with heme in an apolar environment. Our results show that polarization of the porphyrin π-electron cloud by the field from water dipoles influences Em7. The dominant effect of this and other determinates of iron electron availability is perturbations of delocalized electron density in the porphyrin chelate, reproduced by a model where the prosthetic group is treated as a disc of uniform electron density. The present work is also of interest since the interfacial energy constitutes the main barrier for heme-protein separation [9-11].

Place, publisher, year, edition, pages
2000. Vol. 268, no 3, p. 683-687
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Fysik
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URN: urn:nbn:se:ltu:diva-14774DOI: 10.1006/bbrc.2000.2201ISI: 000085640000005Scopus ID: 2-s2.0-0034708126Local ID: e3332c20-f1c3-11db-bb1b-000ea68e967bOAI: oai:DiVA.org:ltu-14774DiVA, id: diva2:987747
Note
Validerad; 2000; 20070423 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved

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