CO Photolysis Research Articles

Strong Depletion of 13C in CO Induced by Photolysis of CO2 in the Martian Atmosphere, Calculated by a Photochemical Model

The isotopic signature of atmospheric carbon offers a unique tracer for the history of the Martian atmosphere and the origin of organic matter on Mars. The photolysis of CO2 is known to induce strong isotopic fractionation of the carbon between CO2 and CO. However, its effects on the carbon isotopic compositions in the Martian atmosphere remain uncertain. Here, we develop a 1D photochemical model to consider the isotopic fractionation via photolysis of CO2, to estimate the vertical profiles of the carbon isotopic compositions of CO and CO2 in the Martian atmosphere. We find that CO is depleted in 13C compared with CO2 at each altitude, due to the fractionation via CO2 photolysis: the minimum value of the δ 13C in CO is about −170‰ under the standard eddy diffusion setting. This result supports the hypothesis that fractionated atmospheric CO is responsible for the production of the 13C-depleted organic carbon in the Martian sediments detected by the Curiosity Rover, through the conversion of CO into organic materials and their deposition on the surface. The photolysis and transport-induced fractionation of CO that we report here leads to a ∼15% decrease in the amount of inferred atmospheric loss when combined with the present-day fractionation of the atmosphere and previous studies of carbon escape to space. The fractionated isotopic composition of CO in the Martian atmosphere may be observed by ExoMars Trace Gas Orbiter and ground-based telescopes, and the escaping ion species produced by the fractionated carbon-bearing species may be detected by the Martian Moons eXploration mission in the future.

Probing the Nitrite Reductase Activity of Heme-Copper Respiratory Oxidase

Heme-copper oxidases, in particular cytochrome ba 3, is capable of reducing NO to N2O and oxidizing CO to CO2, although with a low activity. Despite the very low (20%) overall sequence homology to other structurally known cytochrome c oxidases, the four redox centers of cytochrome ba 3 display high similarity with those of other oxidases. Extensive studies, at ambient temperatures, have shown that the heme a 3-CuB binuclear center of fully reduced (FR) and mixed valence (MV) cytochrome ba 3 is subjected to peculiar thermodynamic and kinetic properties, with significant deviations, relative to the mesophilic aa 3-type oxidases. These properties include an increased hydrophobicity, a high affinity of CuB for exogenous ligands such as CO (K > 104 M-1) and a slow intramolecular ligand transfer to heme a 3 (k = 8 s-1). As a result, cytochrome ba 3 is the only documented oxidase where the binding of CO to CuB is exergonic and accounts for 25-30% of the total enzyme concentration. Furthermore, the proximal and the distal environment of heme a 3 shows a high structural flexibility evidenced from the multiple heme a 3 Fe2+-CO conformers detected in both the FR and MV forms of the enzyme. Time-resolved step-scan FTIR studies showed that after photolysis of CO from heme a 3 2+ the ligand is almost quantitatively transferred to CuB 1+ and the transiently formed CuB 1+-CO complex exhibits an unusual long lifetime of 20 ms (pD 8.50). In addition, the midpoint redox potentials of hemes b and a 3 have been reported in three different studies being inverted, with values of 210/213 and 430/285 mV (versus Normal Hydrogen Electrode (NHE)), respectively. Resonance Raman and FTIR studies of the ligand binding properties of heme-copper oxidases will be presented.References. Discrete Ligand Binding and Electron Transfer Properties of ba 3-Cytochrome c Oxidase from Thermus thermophilus: Evolutionary Adaption to Low Oxygen and ...C Koutsoupakis, T Soulimane, C. Varotsis Accounts of chemical research 52 (5), 1380-139, 2019. The structure of a ferrous heme-nitro species in the binuclear heme a3/CuB center of ba 3-cytochrome c oxidase as determined by resonance Raman spectroscopy Loullis, MR Noor, T Soulimane, E Pinakoulaki Chemical Communications 51 (2), 286-289, 2015.

The Photochemistry of Fe2(S2C3H6)(CO)6(µ-CO) and Its Oxidized Form, Two Simple [FeFe]-Hydrogenase CO-Inhibited Models. A DFT and TDDFT Investigation

FeIFeI Fe2(S2C3H6)(CO)6(µ-CO) (1a–CO) and its FeIFeII cationic species (2a+–CO) are the simplest model of the CO-inhibited [FeFe] hydrogenase active site, which is known to undergo CO photolysis within a temperature-dependent process whose products and mechanism are still a matter of debate. Using density functional theory (DFT) and time-dependent density functional theory (TDDFT) computations, the ground state and low-lying excited-state potential energy surfaces (PESs) of 1a–CO and 2a+–CO have been explored aimed at elucidating the dynamics of the CO photolysis yielding Fe2(S2C3H6)(CO)6 (1a) and [Fe2(S2C3H6)(CO)6]+ (2a+), two simple models of the catalytic site of the enzyme. Two main results came out from these investigations. First, a–CO and 2a+–CO are both bound with respect to any CO dissociation with the lowest free energy barriers around 10 kcal mol−1, suggesting that at least 2a+–CO may be synthesized. Second, focusing on the cationic form, we found at least two clear excited-state channels along the PESs of 2a+–CO that are unbound with respect to equatorial CO dissociation.

Comparison of redox and ligand binding behaviour of yeast and bovine cytochrome c oxidases using FTIR spectroscopy

Redox and CO photolysis FTIR spectra of yeast cytochrome c oxidase WT and mutants are compared to those from bovine and P. denitrificans CcOs in order to establish common functional features. All display changes that can be assigned to their E242 (bovine numbering) equivalent and to weakly H-bonded water molecules. The additional redox-sensitive band reported at 1736 cm−1 in bovine CcO and previously assigned to D51 is absent from yeast CcO and couldn't be restored by introduction of a D residue at the equivalent position of the yeast protein. Redox spectra of yeast CcO also show much smaller changes in the amide I region, which may relate to structural differences in the region around D51 and the subunit I/II interface.

On the photochemistry of Fe2(edt)(CO)4(PMe3)2, a [FeFe]‐hydrogenase model: A DFT/TDDFT investigation

AbstractThe photochemistry of the [FeFe] hydrogenases model [Fe2(edt)(CO)4(PMe3)2] (edt = 1‐2 ethane‐dithiolate, (1) is investigated at Time‐Dependent Density Functional Theory (TDDFT) level, focusing on the effect of the phosphine ligands on the early stages of the photodynamic of the system compared to that of the all CO model Fe2(pdt)(CO)6 (2) (pdt = 1‐3 propanedithiolate). We observed a role of the Fe→S charge transfer for the lower energy singlet transitions, unveiling a photoisomerization pathway between the lowest energy forms while the higher energy excitations are likely involved in the CO dissociation pathways. TDDFT shows that the average Fe‐CO bond elongation in 1 is shorter than that observed in 2, providing the electronic structure rationale on the observation that diiron dithiolates are more photo‐stable with respect to the CO photolysis than the all CO model. This is relevant for catalyst photo‐stability and is an advantageous and thus desirable feature for practical applications of photo‐hydrogen evolution.

Probing the Role of the Heme Distal and Proximal Environment in Ligand Dynamics in the Signal Transducer Protein HemAT by Time-Resolved Step-Scan FTIR and Resonance Raman Spectroscopy.

HemAT is a heme-containing oxygen sensor protein that controls aerotaxis. Time-resolved step-scan FTIR studies were performed on the isolated sensor domain and full-length HemAT proteins as well as on the Y70F (B-helix), L92A (E-helix), T95A (E-helix), and Y133F (G-helix) mutants to elucidate the effect of the site-specific mutations on the ligand dynamics subsequent to CO photolysis. The mutations aimed to perturb H-bonding and electrostatic interactions near the heme Fe-bound gaseous ligand (CO) and the heme proximal environment. Rebinding of CO to the heme Fe is biphasic in the sensor domain and full-length HemAT as well as in the mutants, with the exception of the Y133F mutant protein. The monophasic rebinding of CO in Y133F suggests that in the absence of the H-bond between Y133 and the heme proximal H123 residue the ligand rebinding process is significantly affected. The role of the proximal environment is also probed by resonance Raman photodissociation experiments, in which the Fe-His mode of the photoproduct of sensor domain HemAT-CO is detected at a frequency higher than that of the deoxy form in the difference resonance Raman spectra. The role of the conformational changes of Y133 (G-helix) and the role of the distal L92 and T95 residues (E-helix) in regulating ligand dynamics in the heme pocket are discussed.

Photolysis of Carbonyl Diisocyanate: Generation of Isocyanatocarbonyl Nitrene and Diazomethanone.

The stepwise decomposition of carbonyl diisocyanate, OC(NCO)2 , has been studied by using IR spectroscopy in solid argon matrices at 16 K. Upon irradiation with an ArF laser (λ=193 nm), carbonyl diisocyanate split off CO and furnished a new carbonyl nitrene, OCNC(O)N, in its triplet ground state. Two conformers of the nitrene, syn and anti, that were derived from the two conformers of OC(NCO)2 (62 % syn-syn and 38 % syn-anti) were identified and characterized by combining IR spectroscopy and quantum chemical calculations. Subsequent irradiation with visible light (λ>395 nm) caused the Curtius rearrangement of the nitrene into OCNNCO. In addition to the expected decomposition products, N2 and CO, further photolysis of OCNNCO with the ArF laser yielded NOCN, through a diazomethanone (NNCO) intermediate. To further validate our proposed reaction mechanism, ArF-laser photolysis of the closely related NNNNCO and cyclo-N2 CO in solid argon matrices were also studied. The observations of NOCN and in situ CO-trapped product OCNNCO provided indirect evidence to support the initial generation of NNCO as a common intermediate during the laser photolysis of OCNNCO, NNNNCO, and cyclo-N2 CO.

Mixed quantum-classical simulations of the vibrational relaxation of photolyzed carbon monoxide in a hemoprotein.

We present mixed quantum-classical simulations on relaxation and dephasing of vibrationally excited carbon monoxide within a protein environment. The methodology is based on a vibrational surface hopping approach treating the vibrational states of CO quantum mechanically, while all remaining degrees of freedom are described by means of classical molecular dynamics. The CO vibrational states form the "surfaces" for the classical trajectories of protein and solvent atoms. In return, environmentally induced non-adiabatic couplings between these states cause transitions describing the vibrational relaxation from first principles. The molecular dynamics simulation yields a detailed atomistic picture of the energy relaxation pathways, taking the molecular structure and dynamics of the protein and its solvent fully into account. Using the ultrafast photolysis of CO in the hemoprotein FixL as an example, we study the relaxation of vibrationally excited CO and evaluate the role of each of the FixL residues forming the heme pocket.

The CO Photodissociation and Recombination Dynamics of the W172Y/F282T Ligand Channel Mutant of Rhodobacter sphaeroides aa3 Cytochrome c Oxidase.

In the ligand channel of the cytochrome c oxidase from Rhodobacter sphaeroides (Rs aa3 ) W172 and F282 have been proposed to generate a constriction that may slow ligand access to and from the active site. To explore this issue, the tryptophan and phenylalanine residues in Rs aa3 were mutated to the less bulky tyrosine and threonine residues, respectively, which occupy these sites in Thermus thermophilus (Tt) ba3 cytochrome oxidase. The CO photolysis and recombination dynamics of the reduced wild-type Rs aa3 and the W172Y/F282T mutant were investigated using time-resolved optical absorption spectroscopy. The spectral changes associated with the multiple processes are attributed to different conformers. The major CO recombination process (44 μs) in the W172Y/F282T mutant is ~500 times faster than the predominant CO recombination process in the wild-type enzyme (~23 ms). Classical dynamic simulations of the wild-type enzyme and double mutant showed significant structural changes at the active site in the mutant, including movement of the heme a3 ring-D propionate toward CuB and reduced binuclear center cavity volume. These structural changes effectively close the ligand exit pathway from the binuclear center, providing a basis for the faster CO recombination in the double mutant.

UV-visible spectroscopy of macrocyclic alkyl, nitrosyl and halide complexes of cobalt and rhodium. Experiment and calculation.

Transition metal complexes (NH3)5CoX(2+) (X = CH3, Cl) and L(H2O)MX(2+), where M = Rh or Co, X = CH3, NO, or Cl, and L is a macrocyclic N4 ligand are examined by both experiment and computation to better understand their electronic spectra and associated photochemistry. Specifically, irradiation into weak visible bands of nitrosyl and alkyl complexes (NH3)5CoCH3(2+) and L(H2O)M(III)X(2+) (X = CH3 or NO) leads to photohomolysis that generates the divalent metal complex and ˙CH3 or ˙NO, respectively. On the other hand, when X = halide or NO2, visible light photolysis leads to dissociation of X(-) and/or cis/trans isomerization. Computations show that visible bands for alkyl and nitrosyl complexes involve transitions from M-X bonding orbitals and/or metal d orbitals to M-X antibonding orbitals. In contrast, complexes with X = Cl or NO2 exhibit only d-d bands in the visible, so that homolytic cleavage of the M-X bond requires UV photolysis. UV-Vis spectra are not significantly dependent on the structure of the equatorial ligands, as shown by similar spectral features for (NH3)5CoCH3(2+) and L(1)(H2O)CoCH3(2+).

Microsecond time-resolved absorption spectroscopy used to study CO compounds of cytochrome bd from Escherichia coli.

Cytochrome bd is a tri-heme (b 558, b 595, d) respiratory oxygen reductase that is found in many bacteria including pathogenic species. It couples the electron transfer from quinol to O2 with generation of an electrochemical proton gradient. We examined photolysis and subsequent recombination of CO with isolated cytochrome bd from Escherichia coli in one-electron reduced (MV) and fully reduced (R) states by microsecond time-resolved absorption spectroscopy at 532-nm excitation. Both Soret and visible band regions were examined. CO photodissociation from MV enzyme possibly causes fast (τ<1.5 µs) electron transfer from heme d to heme b 595 in a small fraction of the protein, not reported earlier. Then the electron migrates to heme b 558 (τ∼16 µs). It returns from the b-hemes to heme d with τ∼180 µs. Unlike cytochrome bd in the R state, in MV enzyme the apparent contribution of absorbance changes associated with CO dissociation from heme d is small, if any. Photodissociation of CO from heme d in MV enzyme is suggested to be accompanied by the binding of an internal ligand (L) at the opposite side of the heme. CO recombines with heme d (τ∼16 µs) yielding a transient hexacoordinate state (CO-Fe2+-L). Then the ligand slowly (τ∼30 ms) dissociates from heme d. Recombination of CO with a reduced heme b in a fraction of the MV sample may also contribute to the 30-ms phase. In R enzyme, CO recombines to heme d (τ∼20 µs), some heme b 558 (τ∼0.2–3 ms), and finally migrates from heme d to heme b 595 (τ∼24 ms) in ∼5% of the enzyme population. Data are consistent with the recent nanosecond study of Rappaport et al. conducted on the membranes at 640-nm excitation but limited to the Soret band. The additional phases were revealed due to differences in excitation and other experimental conditions.

Photodissociation of CO isotopologues: Models of laboratory experiments and implications for the solar nebula

AbstractCO photodissociation in the solar nebula and/or parent cloud has been proposed to be the mechanism responsible for forming the 16O‐poor reservoir of the calcium‐aluminum‐rich inclusion (CAI) mixing line. However, laboratory experiments on CO photolysis found a wavelength dependence in the oxygen isotope ratios of the product O atoms, which was interpreted as proof that CO photolysis was not a viable mechanism. Here, I report photochemical simulations of these experiments using line‐by‐line CO spectra to identify the origin of the wavelength dependence. At long wavelengths (&gt;105 nm), the line‐by‐line spectra for isotopic CO can explain the experimental data with a combination of C16O self‐shielding and reduced dissociation probabilities for C18O. At short wavelengths, the greater number of diffuse bands increases the importance of mass‐dependent fractionation, lowering the slope to below unity. The line‐by‐line isotopic spectra are then applied to CO photodissociation in a model solar nebula. Three FUV sources are considered (1) HD 303308, an O4 star in Carina; (2) HD 36981, a B5 star in Orion; and (3) TW Hydrae, a T Tauri star of 10 Myr age. Using reduced dissociation probabilities for C18O based on the photolysis experiments yields nebular water slopes approximately 0.95–1.0 for HD 303308 and TW Hya, and approximately 0.8–1.5 for HD 36981. For the central protostar case (TW Hya) with a simplified treatment of the 2‐D radiative transfer, slopes approximately 0.95–1.0 are obtained, independent of the C18O dissociation probability. Greatly improved measurements of the C17O and C18O cross sections and dissociation probabilities are in progress.

Intersubunit Communication via Changes in Hemoglobin Quaternary Structures Revealed by Time-Resolved Resonance Raman Spectroscopy: Direct Observation of the Perutz Mechanism

Time-resolved resonance Raman spectroscopy was used to investigate intersubunit communication of hemoglobin using hybrid hemoglobin in which nickel was substituted for the heme iron in the β subunits. Changes in the resonance Raman spectra of the α heme and the β Ni-heme groups in the hybrid hemoglobin were observed upon CO photolysis in the α subunit using a probe pulse of 436 and 418 nm, respectively. Temporal evolution of the frequencies of the ν(Fe-His) and the γ7 band of α heme was similar to that of unsubstituted hemoglobin, suggesting that substitution with Ni-heme did not perturb the allosteric dynamics of the hemoglobin. In the β subunits, no structural change in the Ni-heme was observed until 1 μs. In the microsecond regime, temporal evolution of the frequencies of the ν(Ni-His) and the γ7 band of β Ni-heme was observed concomitant with an R → T quaternary change at about 20 μs. The changes in the ν(Fe-His) and ν(Ni-His) frequencies of the α and β subunits with the common time constant of ∼20 μs indicated that the proximal tension imposed on the bond between the heme and the proximal histidine strengthened upon the quaternary changes in both the α and the β subunits concertedly. This observation is consistent with the Perutz mechanism for allosteric control of oxygen binding in hemoglobin and, thus, is the first real-time observation of the mechanism. Protein dynamics and allostery based on the observed time-resolved spectra also are discussed.

Effective Pumping Proton Collection Facilitated by a Copper Site (CuB) of Bovine Heart Cytochrome c Oxidase, Revealed by a Newly Developed Time-resolved Infrared System

X-ray structural and mutational analyses have shown that bovine heart cytochrome c oxidase (CcO) pumps protons electrostatically through a hydrogen bond network using net positive charges created upon oxidation of a heme iron (located near the hydrogen bond network) for O2 reduction. Pumping protons are transferred by mobile water molecules from the negative side of the mitochondrial inner membrane through a water channel into the hydrogen bond network. For blockage of spontaneous proton back-leak, the water channel is closed upon O2 binding to the second heme (heme a3) after complete collection of the pumping protons in the hydrogen bond network. For elucidation of the structural bases for the mechanism of the proton collection and timely closure of the water channel, conformational dynamics after photolysis of CO (an O2 analog)-bound CcO was examined using a newly developed time-resolved infrared system feasible for accurate detection of a single C=O stretch band of α-helices of CcO in H2O medium. The present results indicate that migration of CO from heme a3 to CuB in the O2 reduction site induces an intermediate state in which a bulge conformation at Ser-382 in a transmembrane helix is eliminated to open the water channel. The structural changes suggest that, using a conformational relay system, including CuB, O2, heme a3, and two helix turns extending to Ser-382, CuB induces the conformational changes of the water channel that stimulate the proton collection, and senses complete proton loading into the hydrogen bond network to trigger the timely channel closure by O2 transfer from CuB to heme a3.

Accommodation of CO in the di-heme active site of cytochrome bd terminal oxidase from Escherichia coli

Catalytic mechanisms of reduction of O2 to 2H2O by respiratory terminal oxidases have been extensively investigated. Tri-heme (b558, b595, d) cytochrome bd oxidases presumably utilize a dihemic site composed of high-spin hemes d and b595. We performed a CO photolysis/recombination study of the purified fully reduced cytochrome bd from Escherichia coli. Spectrum of CO photolysis suggests photodissociation of the ligand from heme d and from part of heme b595. This is the first clear evidence of interaction of heme b595 with CO at room temperature. The amount of the heme d-CO species is higher after recombination than before photolysis. In the enzyme population with heme b595 bound to CO, heme d remains unliganded, hence the dihemic O2-reducing pocket in cytochrome bd can bind one rather than two diatomic molecules. Occupancy of the site by one ligand molecule probably blocks access of a second molecule. Thus cytochrome bd exhibits strong negative cooperativity in ligand binding. Immediately after photolysis/recombination CO occupies 100% of the heme d sites, whereas after equilibration, the ligand gets located at heme d in 90–95% and at heme b595 in 5–10% of the cytochrome. The equilibration process is possibly associated with an exchange of heme d endogenous ligand.

Matrix isolation studies of 185 nm light-induced cage reactions of o-chlorobenzaldehyde

VUV light photolysis of o-chlorobenzaldehyde (CBA) has been investigated by infrared spectroscopy in cryogenic Ar and O2 matrices. Previously reported photoinduced rotational isomerization from anti- to syn-CBA was confirmed in the Ar matrix. In addition, absorption bands associated with photoinduced rearrangement to benzoyl chloride were observed accompanying the weak bands due to the CO photolysis product. However, in the reactive O2 matrix, isomerization was observed and there was no evidence of benzoyl chloride formation. A kinetic analysis revealed that rearrangement was a minor process under the present excitation energy. The TD-B3LYP calculations show that as the excitation energy increases the predissociation channel will open and the repulsive 1(π, σC-Cl∗) and 1(n, σC-Cl∗) states are directly achievable by the 185nm excitation. Photoinduced rearrangement will be caused by the reaction of thus dissociated cage pairs.

Assignment of the CO-sensitive carboxyl group in mitochondrial forms of cytochrome c oxidase using yeast mutants

Point mutations of E243D and I67N were introduced into subunit I of a 6histidine-tagged (6H-WT) form of yeast Saccharomyces cerevisiae mitochondrial cytochrome c oxidase. The two mutants (6H-E243DI and 6H-I67NI) were purified and showed ≈50 and 10% of the 6H-WT turnover number. Light-induced CO photolysis FTIR difference spectra of the 6H-WT showed a peak/trough at 1749/1740cm−1, as seen in bovine CcO, which downshifted by 7cm−1 in D2O. The bands shifted to 1736/1762cm−1 in 6H-E243DI, establishing that the carboxyl group affected by CO binding in mitochondrial CcOs is E243. In 6H-I67NI, the trough at 1740cm−1 was shifted to 1743cm−1 and its accompanying peak intensity was greatly reduced. This confirms that the I67N mutation interferes with conformational alterations around E243. This article is part of a Special Issue entitled: 17th European Bioenergetics Conference (EBEC 2012).

An Intermediate Conformational State during Ligand Binding to CytochromecOxidase Detected by Time-resolved Resonance Raman Analyses of Heme Peripheral Groups

A time-resolved resonance Raman analysis shows that the vinyl stretching band (1629 cm−1) of the O2-binding heme of cytochrome c oxidase shifts to 1627 cm−1 instantaneously upon photolysis of CO and remains for at least 5 ms before reaching the static band (1626 cm−1). Within the same time scale, an intermediate vinyl bending mode of another heme appears at 435 cm−1. These results suggest that both hemes cooperatively control O2 binding by forming an intermediate conformation for effective proton pumping.

Bromine-Sensitized Solar Photolysis of CO2

Direct photochemical reduction of CO(2) has generally been accomplished by using transition-metal compounds as electron transfer reagents. Here, we show that elemental bromine can function as an alternative photosensitizer. When sunlight is tightly focused on mixtures of CO(2) and Br(2), in the presence of a polar adsorbent such as silica gel, glass wool, alumina, or titania, a metastable red adduct is formed within seconds and concentrates at the point of illumination. Further illumination causes deposition of a stable black film on the polar adsorbent. Mass spectrometry of the cold-trapped red intermediate shows clusters of peaks corresponding to the expected distribution of isotopomers of C(2)O(4)Br(4)(+), as well as of C(2)O(4)Br(3)(+). DFT computations indicate that the lowest-energy species with the formula C(2)O(4)Br(4) is trans-2,4-dibromo-2,4-dihypobromo-1,3-dioxetane. Formation of this molecule from (2CO(2) + 2Br(2)) would require a minimum of 3 visible photons, two of which would hypothetically be used in formation of as-yet undetected CO(2)Br(2) and the third, in a subsequent photodimerization. By elemental analysis, the final amorphous solid product contains a C/Br atomic ratio >12, suggesting that Br(2) is acting photocatalytically. Even with a poorly optimized optical system, the reaction rate has reached as high as 1.6 mg reduced C with 40 s of solar collection using a 30 cm diameter paraboloid reflector. This rate is consistent with the storage of approximately 1% of incident solar energy.

3I0936 ヘムオキシゲナーゼにおけるCO光解離後の構造変化およびCOの放出経路(ヘム蛋白質,口頭発表)

3I0936 ヘムオキシゲナーゼにおけるCO光解離後の構造変化およびCOの放出経路(ヘム蛋白質,口頭発表)