Ferrous porphyrins in organic solvents. I. Preparation and coordinating properties

Brault, Daniel; Rougée, Michel

doi:10.1021/bi00719a019

Cited by 97 publications

(89 citation statements)

References 18 publications

(34 reference statements)

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“…Therefore, the Fe(III)TPP(Im) intermediate was not observed in the equilibrium reaction [8,9]. Similarly, predominantly six-coordinate iron(II) bis-Im porphyrin model has been observed upon addition of Im to ferrous heme in organic solvents [10].…”

Section: Introductionmentioning

confidence: 97%

The proximal and distal pockets of the H93G myoglobin cavity mutant bind identical ligands with different affinities: Quantitative analysis of imidazole and pyridine binding

Sono

Dawson

2008

Spectroscopy

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Abstract. His93Gly sperm whale myoglobin (H93G Mb) has the proximal histidine ligand removed to create a cavity for exogenous ligand binding, making it a versatile template for the preparation of model heme complexes. In this study, we have measured the first and second ligand binding affinities of imidazole and pyridine to form mono-and bis-ligated ferric and ferrous H93G Mb complexes. Electronic absorption spectroscopy has been utilized to determine the binding affinities for the proximal (K d1 , first ligand) and distal (K d2 , second ligand) pockets of H93G Mb. Magnetic circular dichroism spectroscopy has been used to confirm the identity of the complexes. The binding affinities for the first ligand are one hundred-to one thousand-fold higher than those for the second ligand (K d1 K d2 ) for the same exogenous ligand. This is entirely opposite to what is seen with free heme in organic solvents where K d1 K d2 . Thus, the proximal pocket is the high affinity binding site. The lower affinity for the distal pocket can be attributed to steric hindrance from the distal histidine. This report provides quantitative evidence for differential ligand binding affinities of the proximal and distal pockets of H93G Mb, a unique property that facilitates generation of heme iron derivatives not easily prepared with other heme model systems.

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Section: Introductionmentioning

confidence: 97%

The proximal and distal pockets of the H93G myoglobin cavity mutant bind identical ligands with different affinities: Quantitative analysis of imidazole and pyridine binding

Sono

Dawson

2008

Spectroscopy

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“…Thus, hexacoordinate bis-imidazole complexes are much more stable than the pentacoordinate intermediate (5)(6)(7). Although a much weaker ligand, water competes effectively against the binding of the first imidazole base in aqueous solution, causing the apparent equilibrium dissociation constant to be Ն10 Ϫ2 -10 Ϫ4 M (7). Hemoglobins and myoglobins have evolved to stabilize the mono-imidazole heme complex to facilitate reversible O 2 binding to the sixth coordination position.…”

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confidence: 99%

Waterproofing the Heme Pocket

Liong¹,

Dou

Scott³

et al. 2001

Journal of Biological Chemistry

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“…The heme potential is described in the previous section. The bonding potential of the axial ligands can be rep- (23,24) and iron-oxygen (25) bonds respectively.t A value of 2.4 A-1 is estimated for the parameter a by analyzing the stretching vibrations of transition metal complexes (17). The equilibrium parameters bo are taken as the corresponding observed equilibrium values ( Table 1).…”

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Energy-structure correlation in metalloporphyrins and the control of oxygen binding by hemoglobin.

Warshel¹

1977

Proc. Natl. Acad. Sci. U.S.A.

109

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The contribution of the porphyrin skeleton to the potential energy surface of metalloporphyrins is calculated by the semiempirical method of quantum mechanical extension of the consistent force field to ir electron molecules. This calculation makes it possible to correlate the observed structure of metalloporphyrins with the strain energy of the porphyrin skeleton. It is found that the out-of-plane metal displacement in pentacoordinate heme systems is due to both the restricted size of the porphyrin hole and the "1-3" steric interaction between the axial ligand and the heme nitrogens. The main components of the active site of hemoglobin are simulated by a histidine-heme-oxygen system. The energy surface of this system provides a quantitative explanation for the control of ligand binding by hemoglobin. It is shown that the heme acts as a diaphragm, designed to provide simultaneous binding to the histidine and the sixth ligand under the steric requirements of the 1-3 interactions. The dependence of the hemoglobin potential surface on the distance between the proximal histidine and the heme plane is evaluated for the R and T states, using the calculated heme potential and the observed energy of hemeheme interaction.X-ray and biochemical experiments have provided detailed information about the structure of hemoglobin and its biological functions (for a recent review see ref. 1). Many studies have been concerned with the analysis of the molecular origin of the heme-heme interaction (the increase in the affinity of the fourth bound oxygen relative to that of the first bound oxygen). Perutz and coworkers (2-5) compared the structures of the high and low oxygen affinity states of hemoglobin. They suggested that in the low oxygen affinity state the protein pulls the iron away from the heme plane, and opposes the transition to the low spin state which is needed for combination with oxygen. Hopfield (6) used a simple model of two springs to suggest that the heme-heme interaction energy is distributed among many degrees of freedom in the protein and not in the relatively rigid heme. Experiments (7, 8) have not found evidence for significant strain in the heme group.At the present time, despite the above studies, the role of the active site of hemoglobin in the control of oxygen binding is not fully understood. For example, the reasons for the change in heme geometry upon binding of oxygen and the relation between the heme tension, spin state, and oxygen affinity are still unclear. It is also questionable whether or not the heme group can be considered a rigid system. The analysis of these problems requires information about the energy surface of the heme group and such information cannot be obtained directly from structural or spectroscopic studies.This work uses energy calculations to study the correlation between the energy and structure of the active site system shown in Fig. 1. These quantitative calculations make it possible to examine the molecular basis for the control of oxygen binding by hemoglobin. It is f...

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Ferrous porphyrins in organic solvents. I. Preparation and coordinating properties

Cited by 97 publications

References 18 publications

The proximal and distal pockets of the H93G myoglobin cavity mutant bind identical ligands with different affinities: Quantitative analysis of imidazole and pyridine binding

The proximal and distal pockets of the H93G myoglobin cavity mutant bind identical ligands with different affinities: Quantitative analysis of imidazole and pyridine binding

Waterproofing the Heme Pocket

Energy-structure correlation in metalloporphyrins and the control of oxygen binding by hemoglobin.

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