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A Comparative Study of O2, CO and CN Binding to Heme IX Protein Models
Institut Universitari de Ciència Molecular, Universitat de València, Dr. Moliner 50, E 46100 Burjassot (València), Spain
Received: 26 April 2004; Accepted: 7 June 2004 / Published: 31 July 2004
Abstract: Parametrization of a molecular-mechanics program to include terms specificfor five- and six-coordinate transition metal complexes results in computer-simulatedstructures of heme complexes. The principal new feature peculiar to five and sixcoordination is a term that measures the effect of electron-pair repulsion modified by theligand electronegativity and takes into account the different structural possibilities. Themodel system takes into account the structural differences of the fixing centre in thehaemoglobin subunits. The customary proximal histidine is added. The prosthetic groupheme IX is wholly considered in our model. The calculations show clearly that certainconformations are much more favourable that others for fixing O2. From the O2 bindingin haemoglobin, myoglobin and simple Fe porphyrin models it is concluded that the bentO2 ligand is best viewed as bound superoxide O2–. Axial ligands are practically free-rotating. A small modification of the model in both crystal and protein matrix affects theorientation of the ligands in experimental systems.
Keywords: Electron-pair repulsion; polarizing molecular mechanics; iron–porphyrin complex; oxygen fixation; CO/O2 discrimination.
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Torrens, F. A Comparative Study of O2, CO and CN Binding to Heme IX Protein Models. Molecules 2004, 9, 632-649.
Torrens F. A Comparative Study of O2, CO and CN Binding to Heme IX Protein Models. Molecules. 2004; 9(8):632-649.
Torrens, Francisco. 2004. "A Comparative Study of O2, CO and CN Binding to Heme IX Protein Models." Molecules 9, no. 8: 632-649.