Influence of trans weak or strong field ligands upon the affinity of deuteroheme for carbon monoxide. Monoimidazoleheme as a reference for unconstrained five-coordinate hemoproteins

Rougée, Michel; Brault, Daniel

doi:10.1021/bi00689a028

Cited by 115 publications

(88 citation statements)

References 27 publications

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“…A number of other simple model systems have CO affinities similar to those of the chelated hemes (6,9,19,20) although the corresponding studies with 02 have not been made.…”

Section: Introductionmentioning

confidence: 99%

“…Structural and dynamic studies of hemoproteins have led to three distinct but not necessarily exclusive proposals for the effects of the protein on the reactivity of heme toward 02 and CO. Two of these postulates, the proximal base tension effect (1,2) and the proximal imidazole deprotonation effect (3)(4)(5), have recently been documented by studies of model compounds (6)(7)(8)(9)(10)(11). The third postulate, of a distal side steric effect, has been the subject of some controversy in model compound studies (7,9).…”

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confidence: 99%

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Binding of O2 and CO to hemes and hemoproteins.

Traylor¹,

Berzinis²

1980

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

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Enthalpies and entropies have been determined for the reversible binding of 02 Structural and dynamic studies of hemoproteins have led to three distinct but not necessarily exclusive proposals for the effects of the protein on the reactivity of heme toward 02 and CO. Two of these postulates, the proximal base tension effect (1, 2) and the proximal imidazole deprotonation effect (3-5), have recently been documented by studies of model compounds (6-11). The third postulate, of a distal side steric effect, has been the subject of some controversy in model compound studies (7,9).In hemoproteins studied by x-ray crystallography, the Fell-CO has the ligand "pushed" off the axis by a nearby histidine or other distal side residue (12)(13)(14), in contrast to the observations in simple complexes (15). This effect was postulated to decrease the affinity of CO (16). A corollary suggestion is that Fel-OO, being bent already, should not suffer this steric effect, and CO binding in the hemoproteins should be impaired relative to that in simple model complexes (7,16).In contrast to these predictions, the model compounds chelated protoheme and chelated mesoheme were reported to bind both 02 and CO in aqueous suspension at 20°C with affinities and kinetics similar to those of the high-affinity proteins R-state hemoglobin and hemoglobin chains (8,17,18). A number of other simple model systems have CO affinities similar to those of the chelated hemes (6,9,19,20) although the corresponding studies with 02 have not been made.Based upon these observations we suggested that in R-state hemoglobin or isolated hemoglobin chains the protein served only to keep the heme five-coordinated and to prevent oxidation, imparting no special effect on the heme affinity for CO or 02-Other hemoproteins having lower CO or 02 affinities were presumed to accomplish this alteration from the standard hemoglobin chain behavior by one of the effects mentioned above (18).The more elaborate iron complexes such as cyclophane heme (21,22), capped heme (23), or picket-fence heme (7,24,25), all of which have bulky groups around one face of the heme, either do not mimic the hemoproteins or do so only in part. Picket-fence heme was reported to bind 02 in toluene or in solid state (7) with an affinity similar to that of chelated heme or R-state hemoglobin but to bind CO "irreversibly" in the solid state (24) and with greatly increased affinity in solution (25). These observations led to the conclusion that model compounds bind CO more strongly than do hemoproteins (24), in contrast to the proposal discussed above.We now report the thermodynamics of the binding of 02 and CO (Eqs. 1 and 2) and the replacement reaction (Eq. 3) which are very nearly the same as those of hemoglobin (R-state) Kinetics were determined with a microprocessor-controlled laser flash photolysis apparatus as described (9,26

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“…A number of other simple model systems have CO affinities similar to those of the chelated hemes (6,9,19,20) although the corresponding studies with 02 have not been made.…”

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

Binding of O2 and CO to hemes and hemoproteins.

Traylor¹,

Berzinis²

1980

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

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“…The spectrophotometric titrations of the four-and fivecoordinate Fe(l1) compounds by externally added ligands (including CO) have been performed as previously described (23,24,32). The solubility of CO in benzene at 20°C is assumed to be 6.7 x M atm-' (19).…”

Section: Discussionmentioning

confidence: 99%

“…The abbreviations and notations used throughout are the same as in ref. 32 for the fourcoordinate species, and are derived from them for the fivecoordinate species, as briefly summarized below.…”

Section: Discussionmentioning

confidence: 99%

Five-coordinate iron(II) porphyrins derived from meso-α,β,γ,δ tetraphenylporphin: synthesis, characterization, and coordinating properties

Momenteau¹,

Loock²,

Bisagni³

et al. 1979

Can. J. Chem.

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Meso-cc,fl,y,F,tetraphenylporphin derivatives bearing acrylic (cis and ~rcrt~s isomers) and propionic side chains with a terminal imidazole group have been synthesized. Intermediate conipounds obtained during their preparation were characterized by visible spectroscopy and nmr. In non-coordinating solvents (benzene or toluene), the iron(II1) complexes of these compounds do not show intramolecular coordination of the terminal base on the nietal ion. The reduced forms of the compounds have been obtained from ferric fornis by heterogeneous reduction with aqueous dithionite and exhibit optical spectra characteristic of five-coordinate ferrous complexes. The nitrogenous bases and carbon monoxide affinities of the latter have been measured and the results indicate that the 'trans injlrence' exerted by the terminal iniidazole does not depend greatly on the nature and the structure of the covalent side chain. In contrast the stabiIity of the five-coordinate compounds depends on the side chain (trans acrylic < propionic < cis acrylic) as suggested by the values reported for the replacement constants of the terminal imidazole by 4-cyanopyridine in unsymmetrical six-coordinate derivatives. The stability of these compounds towards oxidation is also reported.MICHEL MOMENTEAU, BERNARD LOOCK, EMILE BISAGNI et MICHEL ROUGEE. Can. J. Chem. 1804(1979). 57,La synthese de composis derives de la tneso-cc,fl,y,F,tetraphenylporphine possedant une chaine acrylique (isomeres cis et trans) ou une chaine propionique et substitute par un groupe imidazole terminal est decrite. Les colnposes intermediaires obtenus au cours de cette synthese sont caracterisks par spectrophotometrie visible et par rmn. Dans les solvants non-coordinants (benzene ou toluene), les complexes ferriques de ces composks ne montrent pas de coordination intramoleculaire de la base terminale sur l'ion metallique. Les formes reduites obtenues par reduction hkterogene des con~plexes ferriques presentent des spectres d'absorption caractkristiques des complexes ferreux pentacoordonnes. Les constantes d'affinite de ces composes pour les bases azotees et le monoxyde de carbone ont ete mesurtes. Elles indiquent que 1"'effet trat~s" exerce par I'imidazole terminal ne depend ni de la nature ni de la structure de la chaine.Au contraire, la stabilite des composes pentacoordonnes en depend (tmns acrylique < propionique < cis acrylique) comme le suggerent les valeurs des constantes de remplacement de I'imidazole par la 4-cyanopyridine dans les derives hexacoordonnes. La stabilite de ces composes vis-a-vis de I'oxydation est Cgalement decrite. IntroductionFor some years, several studies have been made in order to understand the factors controlling the binding of oxygen in oxygen carriers, such as hemoglobin and myoglobin, or in oxygen activating hemoproteins. Synthesis of models for the active sites in these proteins has demonstrated the role of the hydrophobic environment and of the trans coordinating base upon the fixation of oxygen and the stabilization of the resulting oxygen com...

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“…The comparison of wavelength and absorbance ratio between models and the enzyme ( (17,26,27) indicate that solvents such as substituted formamides are slightly coordinated to heme, and although the affinity of these solvents towards heme is low, they are capable of modulating the binding between heme and other strong coordinating ligands. As shown in Scheme I, there is a 2-fold decrease of the formation constants when measured in DMA, and this could be viewed as a solvent coordination effect.…”

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confidence: 99%

Carbon monoxide binding to pentacoordinate mercaptide-heme complexes: kinetic study on models for cytochrome P-450.

Chang¹,

Dolphin²

1976

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

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Mercaptide anions form exclusively pentacoordinate heme complexes [R--hemeJ in polar and nonpolar solution over a wide range of mercaptide concentration. These complexes have a Soret peak at 408 nm and a formation constant of abut 2.5 X 104 M-', and combine with CO to give a CO cytochrome P450 type spectrum. Kinetics and cytochrome P450. The reaction of alkoxide anion with heme has also been examined but no evidence was found for the existence of the [RO--heme-CO] species. Cytochromes P-450 are a unique class of hemeproteins that catalyze the hydroxylation of a wide variety of organic compounds through the activation of molecular oxygen (1, 2). Although the primary locus of such enzyme systems is in the microsomal fraction of mammalian liver and adrenal cortex, much of our present knowledge concerning the properties of P-450 has been obtained from studies on the more readily available soluble P-450 of bacterial origin. A substantial amount of information is now available on the functional aspects of the catalytic reaction but comparatively little is known concerning the structure of the active site of the enzyme itself. Specifically, the nature and roles of axial ligands coordinated to the prosthetic group, protoheme, are yet to be elucidated. In the absence of definitive x-ray crystal structures of P-450, we have undertaken the approach of synthesizing model compounds which mimic P-450, in order that its mechanism of enzymic activities can be elucidated.The absorption spectrum with the unusual red-shifted Soret band of CO-P-450 complex has already been successfully duplicated with simple iron(II) porphyrins by having a mercaptide ion ligated trans to CO, at the fifth coordination site of heme (3-6). This evidence, coupled with earlier electron spin resonance experiments on both enzymes and model compounds (7)(8)(9), strongly implies that a mercaptide ligand is coordinated to all the ferric stages and at some stages of the ferrous complex in the P-450 catalytic cycle. In the absence of CO, our model exhibited a spectrum with absorption bands at wavelengths identical to those of reduced P-450 (3, 4). Since the unligated form of P-450 is assumed to be a pentacoordinate heme with subsequent ligation of CO or 02 taking place at the sixth site, we have examined the reaction between mercaptide ion and heme and studied the properties of the "mono" mercaptideheme species. We wish to report here the thermodynamics and kinetics of the interactions between mercaptide ion, heme, and CO, and to report some observations on the obligatory nature Abbreviations: P-450, cytochrome P-450; DMA, NN-dimethylacetamide; Me2SO, dimethyl sulfoxide; Heme, iron(II) protoporphyrin IX dimethyl ester; Hemin, iron(III) protoporphyrin IX chloride dimethyl ester.of the mercaptide ligand in bringing about the long-wavelength Soret peak of the CO complexes. MATERIALS AND METHODSProtohemin chloride dimethyl ester was prepared by insertion of iron into protoporphyrin IX dimethyl ester, which was synthesized from protoporphyrin via its ...

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Influence of trans weak or strong field ligands upon the affinity of deuteroheme for carbon monoxide. Monoimidazoleheme as a reference for unconstrained five-coordinate hemoproteins

Cited by 115 publications

References 27 publications

Binding of O2 and CO to hemes and hemoproteins.

Binding of O2 and CO to hemes and hemoproteins.

Five-coordinate iron(II) porphyrins derived from meso-α,β,γ,δ tetraphenylporphin: synthesis, characterization, and coordinating properties

Carbon monoxide binding to pentacoordinate mercaptide-heme complexes: kinetic study on models for cytochrome P-450.

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