On the role of the axial ligand in heme proteins: a theoretical study

Research output: Contribution to journalArticle

Abstract

We present a systematic investigation of how the axial ligand in heme proteins influences the geometry, electronic structure, and spin states of the active site, and the energies of the reaction cycles. Using the density functional B3LYP method and medium-sized basis sets, we have compared models with His, His+Asp, Cys, Tyr, and Tyr+Arg as found in myoglobin and hemoglobin, peroxidases, cytochrome P450, and heme catalases, respectively. We have studied 12 reactants and intermediates of the reaction cycles of these enzymes, including complexes with H2O, OH-, O2-, CH3OH, O-2, H2O2, and HO2- in various formal oxidation states of the iron ion (II to V). The results show that His gives similar to0.6 V higher reduction potentials than the other ligands. In particular, it is harder to reduce and protonate the O-2 complex with His than with the other ligands, in accordance with the O-2 carrier function of globins and the oxidative chemistry of the other proteins. For most properties, the trend Cys<Tyr<Tyr+Arg<His+Asp<His is found, reflecting the donor capacity of the various ligands. Thus, it is easier to reduce compound I with a His+Asp ligand than with a Cys ligand, in accordance with the one-electron chemistry of peroxidases and the hydroxylation reactions of cytochromes P450. However, the Tyr complexes have an unusually low affinity for all neutral ligands, giving them a slightly enhanced driving force in the oxidation of H2O2 by compound I.

Details

Authors
Organisations
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Theoretical Chemistry
Original languageEnglish
Pages (from-to)203-223
JournalJournal of Biological Inorganic Chemistry
Volume9
Issue number2
Publication statusPublished - 2004
Publication categoryResearch
Peer-reviewedYes

Bibliographic note

The information about affiliations in this record was updated in December 2015. The record was previously connected to the following departments: Theoretical Chemistry (S) (011001039)