Electronic effects on the binding of dioxygen and carbon monoxide to hemes

Traylor, Teddy G.; White, Dabney K.; Campbell, D. H.; Berzinis, Albin P.

doi:10.1021/ja00406a043

Cited by 45 publications

(14 citation statements)

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“…In addition, it is well known that 02-dissociation rates in haems are sensitive to solvent polarity. The off-rate varies inversely with the solvent polarity, so that as the solvent polarity increases 02 off-rates decrease, an observation consistent with the dipolar nature of the bound 02 (Traylor et al, 1981). Thus it is not unreasonable that nitrosyl autoreduction should also be influenced by haemsite polarity, since the iron-nitrosyl complex is polar (Addison & Stephanos, 1986).…”

Section: Nitrosyl Autoreductionmentioning

confidence: 61%

Haem-binding-site heterogeneity and haem Cotton effects of Glycera dibranchiata monomeric haemoglobins

Difeo

Addison

1989

Biochemical Journal

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The five major components of the monomeric haemoglobin from Glycera dibranchiata were separated and characterized by absorption spectroscopy, isoelectric focusing, azide-binding affinities and nitrosyl autoreduction kinetics. The differences found among the components are discussed in terms of haem-pocket variations. In addition, the Fourier-transform i.r. spectra of pooled monomeric haemoglobin carbonyl (HbmCO) and the major component carbonyl are reported. The c.d. spectra of the carbonyl and azide derivatives of the five components are compared and found to be similar. The c.d. spectra of myoglobin(II) carbonyl [Mb(II)CO] and of apomyoglobin (apoMb) reconstituted with a symmetric synthetic iron porphyrin carbonyl, meso-tetra-(p-carboxyphenyl)porphinatoiron(II) carbonyl [TCPPFe(II)CO], are compared with the c.d. spectra of pooled HbmCO and its TCPPFe(II)CO analogue. HbmTCPPFe(II)CO shows a negative Soret c.d. band whereas MbTCPPFe(II)CO produces both a negative and a positive Soret c.d. band. Displacement of the symmetric porphyrin by 8-anilinonaphthalene-1-sulphonate and the resulting fluorescence emission are reported.

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Section: Nitrosyl Autoreductionmentioning

confidence: 61%

Haem-binding-site heterogeneity and haem Cotton effects of Glycera dibranchiata monomeric haemoglobins

Difeo

Addison

1989

Biochemical Journal

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“…The rate of O 2 binding to the fully reduced FeCuPhOH catalyst is slower than the Fe-only complex possibly because of greater steric hindrance in the former due to the phenol substituent. Note that the O 2 binding rates (step A, Scheme 1) of these complexes are much slower that those reported for C c O and other O 2 binding heme proteins and model complexes 10,11,12. We have recently shown that this slow O 2 binding is due to the presence of an axial water ligand, which H-bonds to additional H 2 O molecules in the distal pocket, making the ferrous catalyst low-spin in nature (Fig.…”

mentioning

confidence: 75%

Catalytic Reduction of O₂ by Cytochrome c Using a Synthetic Model of Cytochrome c Oxidase

et al. 2009

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Cytochrome c oxidase (CcO) catalyzes the four-electron reduction of oxygen to water, the oneelectron reductant Cytochrome c (Cytc) being the source of electrons. Recently we reported a functional model of CcO that electrochemically catalyzes the four-electron reduction of O 2 to H 2 O (Collman et. al. Science, 2007, 315, 1565. The current paper shows that the same functional CcO model will catalyze the four-electron reduction of O 2 using the actual biological reductant Cytc in a homogeneous solution. Both single and steady-state turnover kinetic studies indicate that O 2 binding is rate determining and O-O bond cleavage and electron transfer from reduced Cytc to the oxidized model complex are relatively fast.Cytochrome c oxidase (CcO) performs a four electron reduction of oxygen to water, in the last step of respiration. 1 The active site in CcO is comprised of a heme/Cu site having a post translationally modified tyrosine residue covalently bound to one of the histidine ligands of the distal Cu (Fig. 1A). 2 Cytochrome c (Cytc), a small electron transfer protein, is the source of electrons for CcO. Cytc has a co-ordinatively saturated low-spin heme active site (Fig. 1B). 1 Mimicking the structure and function of CcO using synthetic model complexes has attracted significant attention over the last two decades. 3,4,5 Recently a model of CcO that incorporates a heme with a covalently attached proximal imidazole, a tris-imidazole distal binding pocket for Cu, and a covalently modified tyrosine (Y244) analogue has been reported (FeCuPhOH, Fig. 1C). 6 This functional model catalyzes the selective four electron reduction of oxygen at physiological pH, using an electrode as the source of electrons and generates negligible (<4%) partially reduced oxygen species (PROS) during catalytic turnover. 7 Herein we report the selective catalytic four electron reduction of oxygen by the biological one-electron reductant Cytc (from horse heart) using this functional CcO model in a homogeneous mixed solvent system. This homogeneous reaction was monitored by following the oxidation of reduced Cytc by O 2 in the presence of 2% FeCuPhOH catalyst. Fig. 2 shows the kinetic traces. These data show a decrease in the percentage of reduced Cytc at a pseudo 1st order rate of 1.3×10 −3 s −1 , which is much faster than the slow auto-oxidation of reduced Cytc (~1×10 −5 s −1 ). 8 Monitoring the O 2 concentration of the solution before and after the reaction shows that 3.9±0.1 equivalents of reduced Cytc are oxidized per equivalent of O 2 consumed, indicating that this oxidation process is stoichiometric within error. The rate of catalysis (k obs /[Catalyst]) is pH dependent decreasing from 3.9 ± 0.2 × 10 3 M −1 s −1 between pH 6-7 to 1.8 ± 0.1 × 10 3 M −1 s −1 at pH 8 ( Fig. S1) indicating that protonation may be rate limiting at high pH.Due to limitations in the solubility of Cytc under these experimental conditions only 25 turnovers (i.e. 1 equivalent catalyst:100 equivalents Cytc) could be obtained. 9 The turnover jpc@stanford.edu....

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“…In the case of myoglobin, P 50 equals the equilibrium dissociation constant, since only a single binding process occurs The data were taken from Olson et al [14] and Traylor et al [11][12][13] tochrome oxidase (F0.01 mM). Simple protoheme-imidazole complexes in apolar solvents show an affinity for reversible O 2 binding which is a least 100 times smaller than that for myoglobin (Table 1).…”

Section: Introductionmentioning

confidence: 99%

“…In contrast, the FeCO complex is apolar and unlikely to interact strongly with polar amino acid side chains. Traylor and coworkers argued that the 50-fold increase in oxygen affinity observed when chelated protoheme is taken from benzene and put into myristyltrimethylammonium micelles is due to stabilization of the partial negative charge on the bound O 2 (Table 1) [11][12][13][14]. In this case, the favorable electrostatic interactions are less specific and come from either water bound to the micelles or the quaternary amine.…”

Section: Introductionmentioning

confidence: 99%

Myoglobin discriminates between O2, NO, and CO by electrostatic interactions with the bound ligand

1997

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Most biological substrates have distinctive sizes, shapes, and charge distributions which can be recognized specifically by proteins. In contrast, myoglobin must discriminate between the diatomic gases O 2 , CO, and NO which are apolar and virtually the same size. Selectivity occurs at the level of the covalent Feligand complexes, which exhibit markedly different bond strengths and electrostatic properties. By pulling a water molecule into the distal pocket, His64(E7) 1 inhibits the binding of all three ligands by a factor of F10 compared to that observed for protoheme-imidazole complexes in organic solvents. In the case of O 2 binding, this unfavorable effect is overcome by the formation of a strong hydrogen bond between His64(E7) and the highly polar FeO 2 complex. This favorable electrostatic interaction stabilizes the bound O 2 by a factor of F1000, and the net result is a 100-fold increase in overall affinity compared to model hemes or mutants with an apolar residue at position 64. Electrostatic interaction between FeCO and His64 is very weak, resulting in only a two-to three-fold stabilization of the bound state. In this case, the inhibitory effect of distal pocket water dominates, and a net fivefold reduction in K CO is observed for the wild-type protein compared to mutants with an apolar residue at position 64. Bound NO is stabilized Ftenfold by hydrogen bonding to His64. This favorable interaction with FeNO exactly compensates for the tenfold inhibition due to the presence of distal pocket water, and the net result is little change in K NO when the distal histidine is replaced with apolar residues. Thus, it is the polarity of His64 which allows discrimination between the diatomic gases. Direct steric hindrance by this residue plays a minor role as judged by: (1) the independence of K O 2 , K CO , and K NO on the size of apolar residues inserted at position 64, and (2) the observation of small decreases, not increases, in CO affinity when the mobility of the His64 side chain is increased. Val68(E11) does appear to hinder selectively the binding of CO. However, the extent is no more than a factor of 2-5, and much smaller than electrostatic stabilization of bound O 2 by the distal histidine.

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Electronic effects on the binding of dioxygen and carbon monoxide to hemes

Cited by 45 publications

References 1 publication

Haem-binding-site heterogeneity and haem Cotton effects of Glycera dibranchiata monomeric haemoglobins

Haem-binding-site heterogeneity and haem Cotton effects of Glycera dibranchiata monomeric haemoglobins

Catalytic Reduction of O₂ by Cytochrome c Using a Synthetic Model of Cytochrome c Oxidase

Myoglobin discriminates between O2, NO, and CO by electrostatic interactions with the bound ligand

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Electronic effects on the binding of dioxygen and carbon monoxide to hemes

Cited by 45 publications

References 1 publication

Haem-binding-site heterogeneity and haem Cotton effects of Glycera dibranchiata monomeric haemoglobins

Haem-binding-site heterogeneity and haem Cotton effects of Glycera dibranchiata monomeric haemoglobins

Catalytic Reduction of O2 by Cytochrome c Using a Synthetic Model of Cytochrome c Oxidase

Myoglobin discriminates between O2, NO, and CO by electrostatic interactions with the bound ligand

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Catalytic Reduction of O₂ by Cytochrome c Using a Synthetic Model of Cytochrome c Oxidase