PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Spectroscopy, Mossbauer”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 469 records · Page 26Linked to original sources
PubMed1992

The nickel site in active Desulfovibrio baculatus [NiFeSe] hydrogenase is diamagnetic. Multifield saturation magnetization measurement of the spin state of Ni(II).

The magnetic properties of the nickel(II) site in active Desulfovibrio baculatus (DSM 1743) [NiFeSe] hydrogenase have been measured using the multifield saturation magnetization technique. The periplasmic [NiFeSe] hydrogenase was isolated from bacteria grown in excess selenium in the presence of 57Fe. Saturation magnetization data were collected at three fixed fields (1.375, 2.75, 5.5 tesla) over the temperature range from 2 to 100 K. Mössbauer and EPR spectroscopies were used to characterize the magnetic state of the two [4Fe-4S] clusters of the enzyme and to quantitate the small amounts of iron impurities present in the sample. The nickel(II) site was found to be diamagnetic (low spin, S = 0). In combination with recent results from extended x-ray absorption fine structure studies, this magnetic state indicates that the nickel(II) site of active D. baculatus [NiFeSe] hydrogenase is five-coordinate.

Desulfovibrio↗
PubMed1992

Deferoxamine-induced iron mobilization and redistribution of myocardial iron in cultured rat heart cells: studies of the chelatable iron pool by electron microscopy and Mössbauer spectroscopy.

Iron mobilization by deferoxamine from iron-loaded rat heart cells in culture was studied by electron microscopy and Mössbauer spectroscopy to identify the chelatable iron pool. Studies in which iron 59 was used have shown a diminishing response to deferoxamine with increasing time intervals, which suggests a gradual transit from a more available to a less available storage iron compartment. Mössbauer spectroscopy showed that practically all iron mobilized by deferoxamine was derived from the small (less than 3.0 nm) recently acquired iron particles, which supports the "last-in, first-out" principle. Quantitation of cytosolic ferritin iron particles has shown a highly reproducible increase in cytosolic ferritin iron after deferoxamine treatment. This intracellular redistribution of iron stores is explained either by a reduced transfer of cytosolic ferritin into siderosomes or, more likely, by increased mobilization of membrane-bound iron deposits from insoluble polynuclear iron complexes in siderosomes and their subsequent incorporation into cytosolic ferritin. Thus the protective effect of deferoxamine on iron-loaded heart cells may be twofold: (1) net removal of excess iron by the formation of a stable complex of iron with deferoxamine and its secretion into the extracellular environment and (2) a shift of solubilized iron from membrane-bound deposits into the cytosol where iron is detoxified by its incorporation into the hollow shell of the ferritin protein.

Animals↗
PubMed1991

Formate dehydrogenase from Methylosinus trichosporium OB3b. Purification and spectroscopic characterization of the cofactors.

NAD(+)-coupled formate dehydrogenase has been purified to near-homogeneity from the obligate methanotroph Methylosinus trichosporium OB3b. The inclusion of stabilizing reagents in the purification buffers has resulted in a 3-fold increase in specific activity (98 microM/min/mg; turnover number 600 s-1) and as much as a 25-fold increase in yield over previously reported purification protocols. The enzyme, (molecular weight 400,000 +/- 20,000) is composed of four subunit types (alpha, 98,000; beta, 56,000; gamma, 20,000; delta, 11,500) apparently associated as 2 alpha beta gamma delta protomers. The holoenzyme contains flavin (1.8 +/- 0.2), iron (46 +/- 6), inorganic sulfide (38 +/- 4), and molybdenum (1.5 +/- 0.1). The flavin is optically similar to the common flavin cofactors, but it is chromatographically distinct. Anaerobic incubation of the enzyme with formate, NADH, or sodium dithionite, resulted in approximately 50% reduction of the iron and elicited an electron paramagnetic resonance (EPR) spectrum (approximately 2.5 spins/protomer) from which the spectra of five distinct EPR-active centers could be resolved in the g = 1.94 region. Four of these spectra were characteristic of [Fe-S]x clusters. The fifth (gave = 1.99; approximately 0.1 spins/protomer) was similar to that observed for the molybdenum cofactor of xanthine oxidase, and it exhibited the expected hyperfine splitting when the enzyme was enriched with 95Mo (I = 5/2). Mössbauer spectroscopy showed that all of the iron in the enzyme became reduced upon the addition of a redox mediator, proflavin, to the dithionite reduced enzyme at pH 8.0. Nevertheless, a decrease in the EPR-active spin concentration in the g = 1.94 region of the spectrum occurred and was attributed to the reduction of the molybdenum center to the EPR-silent Mo(IV) state (S = 1). The fully reduced enzyme also exhibited a new species with an S = 3/2 ground state (1-2 spins/protomer). Addition of 50% ethylene glycol to the fully reduced enzyme revealed no new species, but caused an increase in the EPR-detectable spin quantitation to 5-6 spins/protomer. This suggests that cluster spin-spin interactions may occur in both the partially and fully reduced native enzyme.

Amino Acids↗
PubMed1991

Mössbauer spectroscopy of oxygenated haemoglobins.

Murine tetrameric oxyhaemoglobin and insect monomeric erythrocruorin were studied. A doublet with the Lorentz form of lines (delta EQ = 2.22 mm s-1; delta alpha-Fe = 0.27 mm s-1; gamma 1/2 = 0.29 mm s-1) was observed in the oxyhaemoglobin spectrum at 4.2 K. In the 80-170 K interval the doublet components are distorted, but at T greater than 175 K, the lines again become symmetrical. In the 175-210 K region the value of gamma 1/2 is approximately 0.42 mm s-1. The profiles of the oxyhaemoglobin spectra are not dependent on the nature of the samples (blood; whole, or in aqueous or water-glycerol solutions at different pH values), or on the rate at which the latter are frozen. The oxyerythrocruorin spectra in aqueous solution and in a water-glycerol solution at 80 K and 170 K were doublets with Lorentz lines (the delta EQ values are equal to 2.20 mm s-1 and 2.12 mm s-1, respectively). It is concluded that the characteristics of the oxyhaemoglobin spectra reflect the specific electronic and structural properties of the oxy-complex in this protein. It was found that the oxyhaemoglobin spectra are very adequately described by two doublets with equal delta and gamma 1/2 values, but with different delta EQ values and relative intensities. A model is described in which these doublets correspond to two types of hydrogen bond associated with the distal histidine (E7), involving the terminal atom of molecular oxygen and the oxygen atom bound with the haem iron, respectively.

Animals↗
PubMed1991

Electron transfer associated with oxygen activation in the B2 protein of ribonucleotide reductase from Escherichia coli.

Each of the two beta peptides which comprise the B2 protein of Escherichia coli ribonucleotide reductase (RRB2) possesses a nonheme dinuclear iron cluster and a tyrosine residue at position 122. The oxidized form of the protein contains all high spin ferric iron and 1.0-1.4 tyrosyl radicals per RRB2 protein. In order to define the stoichiometry of in vitro dioxygen reduction catalyzed by fully reduced RRB2 we have quantified the reactants and products in the aerobic addition of Fe(II) to metal-free RRB2apo utilizing an oxygraph to quantify oxygen consumption, electron paramagnetic resonance to measure tyrosine radical generation, and Mössbauer spectroscopy to determine the extent of iron oxidation. Our data indicate that 3.1 Fe(II) and 0.8 Tyr122 are oxidized per mol of O2 reduced. Mössbauer experiments indicate that less than 8% of the iron is bound as mononuclear high spin Fe(III). Further, the aerobic addition of substoichiometric amounts of 57Fe to RRB2apo consistently produces dinuclear clusters, rather than mononuclear Fe(III) species, providing the first direct spectroscopic evidence for the preferential formation of the dinuclear units at the active site. These stoichiometry studies were extended to include the phenylalanine mutant protein (Y122F)RRB2 and show that 3.9 mol-equivalents of Fe(II) are oxidized per mol of O2 consumed. Our stoichiometry data has led us to propose a model for dioxygen activation catalyzed by RRB2 which invokes electron transfer between iron clusters.

Electron Transport↗
PubMed1991

Iron oxidation chemistry in ferritin. Increasing Fe/O2 stoichiometry during core formation.

The origin of previously observed variations in stoichiometry of iron oxidation during the oxidative deposition of iron in ferritin has been poorly understood. Knowledge of the stoichiometry of Fe(II) oxidation by O2 is essential to establishing the mechanism of iron core formation. In the present work, the amount of Fe(II) oxidized was measured by Mössbauer spectrometry and the O2 consumed by mass spectrometry. The number of protons produced in the reaction was measured by "pH stat" titration and hydrogen peroxide production by the effect of the enzyme catalase on the measured stoichiometry. For protein samples containing low levels of iron (24 Fe(II)/protein) the stoichiometry was found to be 1.95 +/- 0.18 Fe(II)/O2 with H2O2 being a product, viz. Equation 1. 2Fe2+ + O2 + 4H2O----2FeOOH + H2O2 + 4H+ (1) EPR spin trapping experiments showed no evidence of superoxide radical formation. The stoichiometry markedly increased with additional iron (240-960 Fe/protein), to a value of 4 Fe(II)/O2 as in Equation 2. 4Fe2+ + O2 + 6H2O----4FeOOH + 8H+ (2) As the iron core is progressively laid down, the mechanism of iron oxidation changes from a protein dominated process with H2O2 being the primary product of O2 reduction to a mineral surface dominated process where H2O is the primary product. These results emphasize the importance of the apoferritin shell in facilitating iron oxidation in the early stage of iron deposition prior to significant development of the polynuclear iron core.

Animals↗
PubMed1989

Purification and properties of high potential iron-sulphur protein from Thiocapsa roseopersicina.

High potential iron-sulphur protein (HiPIP) has been purified to electrophoretic homogeneity from the photosynthetic bacterium Thiocapsa roseopersicina. The protein has a single polypeptide chain (molecular mass 10 kDa) containing one 4Fe-4S cluster. The midpoint redox potential (E = 0.35 V), isoelectric points and pH profile, as well as the absorption, circular dichroism and Mössbauer spectroscopic properties in the reduced and oxidized states have been determined. The protein is in the reduced state as isolated; upon oxidation by ferricyanide there are characteristic changes in its visible absorption and circular dichroism spectra. HiPIP contains no alpha helix, about half of the polypeptide chain assumes beta sheet conformation. Pronounced structural differences between the oxidized and reduced states have been observed in the aromatic amino acid and Fe-S cluster spectral regions. Mössbauer spectra of the HiPIP in the two redox states reveal further differences. The possible contribution of aromatic amino acid residues, to the redox transition is discussed.

Bacterial Proteins↗
PubMed1989

Mössbauer and EPR studies of the binuclear iron center in ribonucleotide reductase from Escherichia coli. A new iron-to-protein stoichiometry.

57Fe-enriched ribonucleotide reductase subunit B2 from Escherichia coli strain N6405/pSPS2 has been characterized by Mössbauer and EPR spectroscopy in its native diferric state and in a new differous form. The native protein exhibits two Mössbauer doublets in a 1:1 ratio with parameters that are in excellent agreement with those reported for the wild-type protein (Atkin, C. L., Thelander, L., Reichard, P., and Lang, G. (1983) J. Biol. Chem. 248, 7464-7472); in addition, our studies show the absence of adventitiously bound iron. The iron content in the present samples approached 4 per B2 subunit, and the tyrosyl radical content exceeded 1 per B2 subunit. The higher values are attributed to the use of a new epsilon 280 for the protein and more efficient methods for iron extraction. We thus propose that subunit B2 has two binuclear iron clusters, each associated with its own tyrosyl radical, in contradistinction from the prevailing model. Reduction of the native protein with dithionite or reconstitution of the apoprotein with Fe(II) afforded a protein complex with Mössbauer parameters, delta EQ = 3.13 mm/s and delta = 1.26 mm/s at 4.2 K, and a low field EPR signal associated with an integer spin system. These spectral properties resemble those of methane monooxygenase in its diferrous form. Upon exposure to O2, the reduced subunit B2 readily converts to the diferric state and yields active enzyme.

Dithionite↗
PubMedDate not supplied

[Gamma resonance velocimetry of the eye].

A new method for the registration of ocular orbital pulse in humans is suggested, based on the nuclear gamma resonance effect. In normal subjects the velocity of the corneal movement over the period of a cardiac contraction is under 0.3 mm/s, and the mean amplitude of corneal transposition is 21.8 +/- 0.6 microns. The amplitude of corneal transposition and the cardiac cycle length are in square relationship.

Adolescent↗
PubMed1988

The CO adduct of yeast cytochrome c oxidase. Mössbauer and photolysis studies.

Mössbauer spectra of 57Fe-enriched NADH-reduced yeast cytochrome c oxidase reveal two quadrupole doublets of unequal intensity; one (approximately 33%) is typical of high-spin ferrous heme with histidine coordination and is assigned to heme a3, while the other (approximately 67%) is typical of low-spin heme with two nitrogeneous axial ligands as expected from heme a. The excess intensity (approximately 17%) of the low-spin doublet must therefore be assigned to heme a3 in a modified environment. The Mössbauer spectra of the same sample exposed to CO show that 50% of the heme iron forms a CO adduct, consistent with heme a3 being inhibited by CO. While low-spin hem a has the same Mössbauer parameters as in the reduced sample, its intensity has dropped to 35%. A distinctly new high-spin species (approximately 15%) is observed and assigned to heme a in a modified environment. The comparable size of the unexpected high-spin heme a fraction in the CO adduct and the low-spin heme a3 fraction in the reduced enzyme suggest that they arise from the same material. This material is likely to be the inactive fraction that has been found in all preparations of resting yeast cytochrome c oxidase (Siedow, J.N., Miller, S., and Palmer, G. (1981) J. Bioenerg. Biomembr. 14, 171-179). The kinetics of CO recombination following photolysis of the CO complex further confirms the coexistence of two distinct fractions associated with active and inactive protein. The majority (approximately 74%), presumably active protein, recombines exponentially from 160 to 270 K following an Arrhenius law. The large activation enthalpy, delta H approximately 35 kJ/mol, is comparable to that found in the beef heart enzyme, suggesting that the flashed-off CO is bound by the nearby CuB as in the mammalian system (Fiamingo, F.G., Altschuld, R.A., Moh, P.P., and Alben, J.O. (1982) J. Biol. Chem. 250, 1639-1650). In the minority, presumably inactive, fraction the CO recombination has fast nonexponential kinetics with a distribution of activation enthalpies peaking near delta Hp = 13 kJ/mol reminiscent of CO binding to myoglobin. In this inactive fraction CuB is apparently not accessible to the flashed-off CO.

Algorithms↗
PubMedDate not supplied

[A study of the dynamic properties of membrane proteins using Mössbauer spectroscopy].

While studying the parameters of "narrow" and "broad" lines appearing in Mössbauer spectra of undehydrated membrane proteins heated from 80 to 280 K it has been for the first time found for proteins that the behavior of the complete area of spectrum S does not differ from that of Debye-Waller factor. An abrupt decrease of quadrupole splitting value from delta = 0.7 mm/s to delta = 0 within the temperature range 220-270 K. Computation of the spectra with their division into 3 components responding respectively by heat, diffusion and conformational movement made possible explanation of all the evolutionary changes proceeding in them with the temperature rise. Preservation of the complete area of the spectrum S (T) is conditioned by the increase of the component responsive to conformational changes of Fe atom within 230-270 K. These movements "suppress" quadrupole splitting observed in the spectra at low temperatures. Dynamic mobility is considered in terms of the Fe atom movement in the biphase potential.

Cells, Cultured↗
PubMed1994

Mössbauer characterization of the metal clusters in Azotobacter vinelandii nitrogenase VFe protein.

The VFe protein of alternative nitrogenase, isolated from Azotobacter vinelandii, strain LS15 and designated as Av1', has been investigated by Mössbauer spectroscopy. The Mössbauer spectrum of the dithionite-reduced Av1', recorded at 4.2 K with a 60-millitesla magnetic field applied parallel to the gamma-beam, is a superposition of three spectral components: 1) a complex spectrum (the M component) with magnetic hyperfine structures attributed to the paramagnetic FeV cofactor, 2) a component (the P component) consisting of three quadrupole doublets identifiable as the Fe2+, D, and S doublets similar to those observed for the P cluster pairs in MoFe proteins, and 3) a minor (4% of total absorption) quadrupole doublet attributable to adventitiously bound iron. The observed 4.2-K parameters for the Fe2+ (delta EQ = 2.99 mm/s and delta = 0.64 mm/s), D (delta EQ = 0.75 mm/s and delta = 0.63 mm/s), and S (delta EQ = 1.2 mm/s and delta = 0.65 mm/s) iron sites and their temperature dependence are very similar to those observed for the P cluster pairs in the conventional MoFe proteins. Similar to those of the MoFe protein, strong field spectra indicate that these doublets are associated with a diamagnetic system. Their percent absorption intensities (Fe(2+)/D/S = 13.0:32.2:6.8) determined at 4.2 K after the removal of the contributions from the adventitiously bound iron are comparable to those of the P cluster pairs in MoFe proteins. These observations established that Av1' also contains P cluster pairs that are identical, in both composition and quantity, to those of the MoFe proteins; i.e. each molecule contains two P cluster pairs and each pair is formed by two Fe2+, five D, and one S iron sites. Considering that 52% absorption of the P component corresponding to two 8Fe clusters, the remaining 48% absorption determined for the M component is consistent with two 7Fe-containing FeV cofactors/molecule of Av1'. The fact that both P cluster pairs are found in the diamagnetic states implies that the S = 3/2 and S = 1/2 signals detected in earlier EPR measurements are associated with the FeV cofactor and suggests a spin mixture for the FeV cofactor in the dithionite-reduced Av1'.

Azotobacter vinelandii↗
PubMed1994

Mammalian ferrochelatase, a new addition to the metalloenzyme family.

A [2Fe-2S] cluster has been detected in mammalian ferrochelatase, the terminal enzyme of the heme biosynthetic pathway. Natural ferrochelatase, purified from mouse livers, and recombinant ferrochelatase, purified from an overproducing strain of Escherichia coli, were investigated by electron paramagnetic resonance (EPR) and Mössbauer spectroscopy. In their reduced forms, both the natural and recombinant ferrochelatases exhibited an identical EPR signal with g values (g = 2.00, 1.93, and 1.90) and relaxation properties typical of [2Fe-2S]+ cluster. Mössbauer spectra of the recombinant ferrochelatase, purified from a strain of E. coli cells transformed with a plasmid encoding murine liver ferrochelatase and grown in 57Fe-enriched medium, demonstrated unambiguously that the cluster is a [2Fe-2S] cluster. No change in the cluster oxidation state was observed during catalysis. The putative protein binding site for the Fe-S cluster in mammalian ferrochelatases is absent from the sequences of the bacterial and yeast enzymes, suggesting a possible role of the [2Fe-2S] center in regulation of mammalian ferrochelatases.

Amino Acid Sequence↗
PubMed1994

Thiol/disulfide formation associated with the redox activity of the [Fe3S4] cluster of Desulfovibrio gigas ferredoxin II. 1H NMR and Mössbauer spectroscopic study.

Desulfovibrio gigas ferredoxin II (FdII) is a small protein (alpha 4 subunit structure as isolated; M(r) approximately 6400 per subunit; 6 cysteine residues) containing one Fe3S4 cluster per alpha-subunit. The x-ray structure of FdII has revealed a disulfide bridge formed by Cys-18 and Cys-42 approximately 13 A away from the center of the cluster; moreover, the x-ray structure indicates that Cys-11 forms a disulfide bridge with a methanethiol. In the oxidized state, FdIIoxm the 1H NMR spectra, exhibit four low-field contact-shifted resonances at 29, 24, 18, and 15.5 ppm whereas the reduced state, FdIIR (S = 2), yields two features at +18.5 and -11 ppm. In the course of studying the redox behavior of FdII, we have discovered a stable intermediate, FdIIint, that yields 1H resonances at 24, 21.5, 21, and 14 ppm. This intermediate appears in the potential range where the cluster (E'0 approximately -130 mV) is reduced from the [Fe3S4]1+ to the [Fe3S4]0 state. FdIIint is observed during reductive titrations with dithionite or hydrogen/hydrogenase or after partial oxidation of FdIIR by 2,6-dichlorophenolindophenol or air. Our studies show that a total of three electrons per alpha-subunit are transferred to FdII. Our experiments demonstrate the absence of a methanethiol-Cys-11 linkage in our preparations, and we propose that two of the three electrons are used for the reduction of the disulfide bridge. Mössbauer (and EPR) studies show that the Fe3S4 cluster of FdIIint is at the same oxidation level as FdIIox, but indicate some changes in the exchange couplings among the three ferric sites. Our data suggest that the differences in the NMR and Mössbauer spectra of FdIIox and FdIIint result from conformational changes attending the breaking or formation of the disulfide bridge. The present study suggests that experiments be undertaken to explore an in vivo redox function for the disulfide bridge.

Desulfovibrio↗
PubMed1994

Spectroscopic properties of desulfoferrodoxin from Desulfovibrio desulfuricans (ATCC 27774).

Desulfoferrodoxin, a non-heme iron protein, was purified previously from extracts of Desulfovibrio desulfuricans (ATCC 27774) (Moura, I., Tavares, P., Moura, J. J. G., Ravi, N., Huynh, B. H., Liu, M.-Y., and LeGall, J. (1990) J. Biol. Chem. 265, 21596-21602). The as-isolated protein displays a pink color (pink form) and contains two mononuclear iron sites in different oxidation states: a ferric site (center I) with a distorted tetrahedral sulfur coordination similar to that found in desulforedoxin from Desulfovibrio gigas and a ferrous site (center II) octahedrally coordinated with predominantly nitrogen/oxygen-containing ligands. A new form of desulfoferrodoxin which displays a gray color (gray form) has now been purified. Optical, electron paramagnetic resonance (EPR), and Mössbauer data of the gray desulfoferrodoxin indicate that both iron centers are in the high-spin ferric states. In addition to the EPR signals originating from center I at g = 7.7, 5.7, 4.1, and 1.8, the gray form of desulfoferrodoxin exhibits a signal at g = 4.3 and a shoulder at g = 9.6, indicating a high-spin ferric state with E/D approximately 1/3 for the oxidized center II. Redox titrations of the gray form of the protein monitored by optical spectroscopy indicate midpoint potentials of +4 +/- 10 and +240 +/- 10 mV for centers I and II, respectively. Mössbauer spectra of the gray form of the protein are consistent with the EPR finding that both centers are high-spin ferric and can be analyzed in terms of the EPR-determined spin Hamiltonian parameters. The Mössbauer parameters for both the ferric and ferrous forms of center II are indicative of a mononuclear high spin iron site with octahedral coordination and predominantly nitrogen/oxygen-containing ligands. Resonance Raman studies confirm the structural similarity of center I and the distorted tetrahedral FeS4 center in desulforedoxin and provide evidence for one or two cysteinyl-S ligands for center II. On the basis of the resonance Raman results, the 635 nm absorption band that is responsible for the gray color of the oxidized protein is assigned to a cysteinyl-S-->Fe(III) charge transfer transition localized on center II. The novel properties and possible function of center II are discussed in relation to those of mononuclear iron centers in other enzymes.

Desulfovibrio↗
PubMed1995

Resonant cell assemblies: a new approach to cognitive functions and neuronal synchrony.

This paper presents a novel reading of ideas on temporal binding as a key for cognitive operations by means of fast (gamma band) phase synchrony. We advocate a view of binding of widely distributed cell assemblies transiently locked in a neural hypergraph which serves as a reference point to incorporate or interpret other less coherent concurrent neural events. The paper traces in some detail the empirical evidence concerning the gamma binding process and presents some implications for the constitution of a unified cognitive-mental space.

Animals↗
PubMed1996

Redox properties of cytochrome c nitrite reductase from Desulfovibrio desulfuricans ATCC 27774.

The dissimilatory nitrite reductase from Desulfovibrio desulfuricans ATCC 27774 catalyzes the reduction of nitrite to ammonia. Previous spectroscopic investigation revealed that it is a hexaheme cytochrome containing one high spin ferric heme and five low spin ferric hemes in the oxidized enzyme. The current study uses the high resolution of Mössbauer spectroscopy to obtain redox properties of the six heme groups. Correlating the Mössbauer findings with the EPR data reveals the pairwise spin-spin coupling among four of the heme groups. The other two hemes are found to be magnetically isolated. Reduction with dithionite and reaction with CO further indicate that only the high spin heme is capable of binding small exogenous ligands. These results confirm our previous finding that Desulfovibrio desulfuricans nitrite reductase contains six heme groups and that the high spin ferric heme is the substrate and inhibitor binding site.

Carbon Monoxide↗