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Davydov RM, Jennings G, Hoffman BM, Podust LM. Short-lived neutral FMN and FAD semiquinones are transient intermediates in cryo-reduced yeast NADPH-cytochrome P450 reductase. Arch Biochem Biophys 2019; 673:108080. [PMID: 31445894 DOI: 10.1016/j.abb.2019.108080] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2019] [Revised: 08/14/2019] [Accepted: 08/20/2019] [Indexed: 11/28/2022]
Abstract
The electron configuration of flavin cofactors, FMN and FAD, is a critical factor governing the reactivity of NADPH-cytochrome P450 reductase (CPR). The current view of electron transfer by the mammalian CPR, based on equilibrium redox potentials of the flavin cofactors, is that the two electron-reduced FMN hydroquinone (FMNH2), rather than one electron-reduced FMN semiquinone, serves as electron donor to the terminal protein acceptors. However, kinetic and thermodynamic studies on the CPR species originated from different organisms have shown that redox potentials measured at distinct electron transfer steps differ from redox potentials determined by equilibrium titration. Collectively, previous observations suggest that the short-lived transient semiquinone species may carry electrons in diflavin reductases. In this work, we have investigated spectroscopic properties of the CPR-bound FAD and FMN reduced at 77 K by radiolytically-generated thermalized electrons. Using UV-vis spectroscopy, we demonstrated that upon cryo-reduction of oxidized yeast CPR (yCPR) containing an equimolar ratio of both FAD and FMN, or FAD alone, neutral semiquinones were trapped at 77 K. During annealing at the elevated temperatures, unstable short-lived neutral semiquinones relaxed to spectroscopically distinct air-stable neutral semiquinones. This transition was independent of pH within the 6.0-10.7 range. Our data on yeast CPR are in line with the previous observations of others that the flavin short-lived transient semiquinone intermediates may have a role in the electron transfer by CPR at physiological conditions.
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Affiliation(s)
- Roman M Davydov
- The Department of Chemistry, Northwestern University, Evanston, IL, USA
| | - Gareth Jennings
- Center for Discovery and Innovation in Parasitic Diseases, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, La Jolla, CA, USA
| | - Brian M Hoffman
- The Department of Chemistry, Northwestern University, Evanston, IL, USA
| | - Larissa M Podust
- Center for Discovery and Innovation in Parasitic Diseases, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, La Jolla, CA, USA.
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Active intermediates in heme monooxygenase reactions as revealed by cryoreduction/annealing, EPR/ENDOR studies. Arch Biochem Biophys 2010; 507:36-43. [PMID: 20854788 DOI: 10.1016/j.abb.2010.09.013] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2010] [Revised: 09/13/2010] [Accepted: 09/14/2010] [Indexed: 11/21/2022]
Abstract
This review describes the use of cryoreduction/annealing EPR/ENDOR techniques for determining the active oxidizing species in reactions catalyzed by heme monooxygenases. The three candidate heme states are: ferric peroxo, ferric hydroperoxo and compound I intermediates. The enzymes discussed include cytochromes P450, nitric oxide synthase and heme oxygenase.
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Davydov R, Hoffman BM. EPR and ENDOR studies of Fe(II) hemoproteins reduced and oxidized at 77 K. J Biol Inorg Chem 2007; 13:357-69. [PMID: 18058139 DOI: 10.1007/s00775-007-0328-5] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2007] [Accepted: 11/14/2007] [Indexed: 11/24/2022]
Abstract
gamma-irradiation of frozen solutions of Fe(II) hemoproteins at 77 K generates both electron paramagnetic resonance (EPR) active singly reduced and oxidized heme centers trapped in the conformation of the Fe(II) precursors. The reduction products of pentacoordinate (S = 2) Fe(II) globins, peroxidases and cytochrome P450cam show EPR and electron-nuclear double resonance (ENDOR) spectra characteristic of (3d 7) Fe(I) species. In addition, cryoreduced Fe(II) alpha-chains of hemoglobin and myoglobin exhibit an S = 3/2 spin state produced by antiferromagnetic coupling between a porphyrin anion radical and pentacoordinate (S = 2) Fe(II). The spectra of cryoreduced forms of Fe(II) hemoglobin alpha-chains and deoxymyoglobin reveal that the Fe(II) precursors adopt multiple conformational substates. Reduction of hexacoordinate Fe(II) cytochrome c and cytochrome b5 as well as carboxy complexes of deoxyglobins produces only Fe(II) porphyrin pi-anion radical species. The low-valent hemoprotein intermediates produced by cryoreduction convert to the Fe(II) states at T > 200 K. Cryogenerated Fe(III) cytochrome c and cytochrome b5 have spectra similar to these for the resting Fe(III) states, whereas the spectra of the products of cryooxidation of pentacoordinate Fe(II) globins and peroxidases are different. Cryooxidation of CO-Fe(II) globins generates Fe(III) hemes with quantum-mechanically admixed S = 3/2, 5/2 ground states. The trapped Fe(III) species relax to the equilibrium ferric states upon annealing at T > 190 K. Both cryooxidized and reduced centers provide very sensitive EPR/ENDOR structure probes of the EPR-silent Fe(II) state.
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Affiliation(s)
- Roman Davydov
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Tech K148, Evanston, IL 60208-3113, USA.
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Denisov IG, Makris TM, Sligar SG. Cryoradiolysis for the study of P450 reaction intermediates. Methods Enzymol 2003; 357:103-15. [PMID: 12424902 DOI: 10.1016/s0076-6879(02)57670-9] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Affiliation(s)
- Ilia G Denisov
- Department of Biochemistry, University of Illinois, Urbana, Illinois 61801, USA
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Denisov IG, Hung SC, Weiss KE, McLean MA, Shiro Y, Park SY, Champion PM, Sligar SG. Characterization of the oxygenated intermediate of the thermophilic cytochrome P450 CYP119. J Inorg Biochem 2001; 87:215-26. [PMID: 11744059 DOI: 10.1016/s0162-0134(01)00328-2] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Using UV-Vis, resonance Raman, and EPR spectroscopy we have studied the properties of the oxygenated ferrous cytochrome P450 from Sulfolobus solfataricus, (CYP119). The recently determined crystal structure of CYP119 is compared with other available structures of P450s, and detailed structural and spectroscopic analyses are reported. With several structural similarities to CYP102, such as in-plane iron position and a shorter iron-proximal ligand bond, CYP119 shows low-spin conformation preference in the ferric form and partially in the ferrous form at low temperatures. These structural features can explain the fast autoxidation of the oxyferrous complex of CYP119. Finally, we report the first UV-Vis and EPR spectra of the cryoradiolytically reduced oxygenated intermediate of CYP119. The primary reduced intermediate, a hydroperoxo-ferric complex of CYP119, undergoes a 'peroxide shunt' pathway during gradual annealing at 170-195 K and returns to the low-spin ferric form.
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Affiliation(s)
- I G Denisov
- Departments of Biochemistry and Chemistry, College of Medicine, and The Beckman Institute, University of Illinois, Urbana, IL 61801, USA
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Denisov IG, Makris TM, Sligar SG. Cryotrapped reaction intermediates of cytochrome p450 studied by radiolytic reduction with phosphorus-32. J Biol Chem 2001; 276:11648-52. [PMID: 11152470 DOI: 10.1074/jbc.m010219200] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Unstable reaction intermediates of the cytochrome P450 catalytic cycle have been prepared at cryogenic temperatures using radiolytic one-electron reduction of the oxy-P450 CYP101 complex. Since a rate-limiting step in the catalytic cycle of the enzyme is the reduction of the ferrous oxygenated heme protein, subsequent reaction intermediates do not normally accumulate. Using (60)Co gamma-irradiation, the primary reduced oxy-P450 species at 77 K has been identified as a superoxo- or hydroperoxo-Fe(3+)-heme complex (Davydov, R., Macdonald, I. D. G., Makris, T. M., Sligar, S. G., and Hoffman, B. M. (1999) J. Am. Chem. Soc. 121, 10654-10655). The electronic absorption spectroscopy is an essential tool to characterize cytochrome P450 intermediates and complements paramagnetic methods, which are blind to important diamagnetic or antiferromagnetically coupled states. We report a method of trapping unstable states of redox enzymes using phosphorus-32 as an internal source of electrons. We determine the UV-visible optical spectra of the reduced oxygenated state of CYP101 and show that the primary intermediate, a hydroperoxo-P450, is stable below 180 K and converts smoothly to the product complex at approximately 195 K. In the course of the thermal annealing, no spectral changes indicating the presence of oxoferryl species (the so-called compound I type spectrum) was observed.
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Affiliation(s)
- I G Denisov
- Department of Biochemistry, Center for Biophysics and Computational Biology, and Beckman Institute, University of Illinois, Urbana-Champaign, Illinois 61801, USA
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Rifkind JM, Abugo O, Levy A, Heim J. Detection, formation, and relevance of hemichromes and hemochromes. Methods Enzymol 1994; 231:449-80. [PMID: 8041268 DOI: 10.1016/0076-6879(94)31030-0] [Citation(s) in RCA: 84] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- J M Rifkind
- Laboratory of Cellular and Molecular Biology, National Institutes of Health, National Institute on Aging, Baltimore, Maryland 21224
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Kaminskaya O, Konstantinov AA, Shuvalov V. Low-temperature photooxidation of cytochrome c in reaction centre complexes from Rhodopseudomonas viridis. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1990. [DOI: 10.1016/0005-2728(90)90054-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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McGourty JL, Peterson-Kennedy SE, Ruo WY, Hoffman BM. Characterization of long-range electron transfer in mixed-metal [zinc,iron] hybrid hemoglobins. Biochemistry 1987; 26:8302-12. [PMID: 3442655 DOI: 10.1021/bi00399a042] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Measurements characterizing electron transfer from a photoexcited zinc protoporphyrin triplet (3ZnP) to a ferriheme electron acceptor within the [alpha 1,beta 2] electron-transfer complex of [FeIII,Zn] hybrid hemoglobins are reported. Analytical results demonstrate that the hybrids studied are pure, homogeneous proteins with 1:1 ZnP:FeP content. Within the T quaternary structure adopted by these hybrids, the optical spectrum of a FeIIIP is perturbed by the protein environment. Room temperature kinetic studies of the rate of 3ZnP decay as a function of the heme oxidation and ligation state demonstrate that quenching of 3ZnP by FeIII(H2O)P occurs by long-range intramolecular electron transfer with rate constant kt = 100 (+/- 10) s-1 and is not complicated by spin-quenching or energy-transfer processes; results are the same for alpha(Zn) and beta(Zn) hybrids. Replacement of H2O as a ligand to the ferriheme changes the 3ZnP----FeIIIP electron-transfer rate constant, kt, which demonstrates that electron transfer, not conformational conversion, is rate limiting. However, the trend is not readily explained by simple considerations of spin-state and bonding geometry: kt decreases in the order imidazole greater than H2O greater than F- approximately CN- approximately N3-. The reverse electron-transfer process FeIIP----ZnP+ has not been observed directly but has been shown to be much more rapid, with rate constant kb greater than 10(3) s-1, consistent with the possible importance of "hole" superexchange in electron tunneling within protein complexes.
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Affiliation(s)
- J L McGourty
- Department of Chemistry, Northwestern University, Evanston, Illinois 60201
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Läuger P. Thermodynamic and kinetic properties of electrogenic ion pumps. BIOCHIMICA ET BIOPHYSICA ACTA 1984; 779:307-41. [PMID: 6089889 DOI: 10.1016/0304-4157(84)90015-7] [Citation(s) in RCA: 80] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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11
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Sharonov YA, Sharonova NA, Figlovsky VA, Grigorjev VA. A comparison of the heme electronic states in equilibrium and nonequilibrium protein conformations of high-spin ferrous hemoproteins. Low temperature magnetic circular dichroism studies. BIOCHIMICA ET BIOPHYSICA ACTA 1982; 709:332-41. [PMID: 6295493 DOI: 10.1016/0167-4838(82)90476-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The visible and near infrared magnetic circular dichroism (MCD) spectra of equilibrium high-spin ferrous derivatives of myoglobin, hemoglobin, horseradish peroxidase and mitochondrial cytochrome c oxidase at 15 K are compared with those of the corresponding proteins in nonequilibrium conformations produced by low-temperature photodissociation of CO-complexes of these proteins as well as of O2-complexes of myoglobin and hemoglobin. Over all the spectral region (450-800 nm) the intensities of MCD bands of hemoproteins studied in equilibrium conformation are shown to be strongly temperature-dependent, including a negative band at ca. 630 nm and positive bands at ca. 690 nm and at ca. 760 nm. In contrast to the absorption spectra, the low-temperature MCD spectra of high-spin ferrous hemoproteins differ significantly, reflecting the peculiarities in the heme iron coordination sphere which are created by a protein conformation. The MCD spectra reveal clearly the structural changes in the heme environment which occur on ligand binding. On the basis of assignment of d leads to d and charge-transfer transitions in the near infrared region the correlation is suggested between the wavelength position of the MCD band at approx. 690 nm and the value of iron out-of-plane displacement as well as between the location of the band at approx. 760 nm and the Fe-N epsilon (proximal histidine) bond strength (length) in equilibrium and nonequilibrium conformations of the hemoproteins studied. The high sensitivity of low-temperature MCD spectra to geometry at heme iron is discussed.
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Alben JO, Beece D, Bowne SF, Doster W, Eisenstein L, Frauenfelder H, Good D, McDonald JD, Marden MC, Moh PP, Reinisch L, Reynolds AH, Shyamsunder E, Yue KT. Infrared spectroscopy of photodissociated carboxymyoglobin at low temperatures. Proc Natl Acad Sci U S A 1982; 79:3744-8. [PMID: 6954517 PMCID: PMC346503 DOI: 10.1073/pnas.79.12.3744] [Citation(s) in RCA: 137] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
We have studied the infrared spectra of the bound and photodissociated states of Mb-12CO and Mb-13CO from 5.2 to 300 K. The absorbance peaks seen between 1800 and 2200 cm-1 correspond to CO stretching vibrations. In the bound state of Mb-12CO, the known lines A0 at 1969, A1 at 1945, and A2 at 1927 cm-1, have center frequencies, widths, and absorbances that are independent of temperature between 5.2 and 160 K. Above 160 K, A2 gradually shifts to 1933 cm-1. The low-temperature photodissociated state (Mb) shows three lines (B0, B1, B2) at 2144, 2131, and 2119 cm-1 for 12CO. The absorbances of the three lines depend on temperature. B0 is tentatively assigned to free CO in the heme pocket and B1 and B2, to CO weakly bound to the heme or heme pocket wall. The data are consistent with a model in which photodissociation of MbCO leads to B1 and B2. B2 decays thermally to B1 above 13 K; rebinding to A occurs from B1. The barriers between B2 and B1 and between B1 and A are described by activation enthalpy spectra. Heme and the central metal atom in state Mb have near-infrared, EPR, and Mössbauer spectra that differ slightly from those of deoxyMb. The observation of essentially free CO in state B implies that the difference between Mb and deoxyMb is not due to an interaction of the flashed-off ligand with the protein but is caused by an incomplete relaxation of the protein structure at low temperatures.
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Greschner S. Absorption spectra of highly purified liver microsomal cytochrome P-450 in non-equilibrium conformational states at low temperatures. BIOPHYSICS OF STRUCTURE AND MECHANISM 1982; 9:29-34. [PMID: 7171721 DOI: 10.1007/bf00536013] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Absorption spectra of highly purified liver microsomal cytochrome P-450 in non-equilibrium states were obtained at 77 K by reduction with trapped electrons, formed by gamma-irradiation of the water-glycerol matrix. In contrast to the equilibrium form of ferrous cytochrome P-450 with the heme iron in the high-spin state the non-equilibrium ferrous state has a low-spin heme iron. The absorption spectrum of the non-equilibrium ferrous cytochrome P-450 is characterized by two bands at 564 (alpha-band) and 530 nm (beta-band). When the temperature is increased to about 278 K this non-equilibrium form of the reduced enzyme is relaxed to the corresponding equilibrium form with a single absorption band at 548 nm in the visible region characteristic for a high-spin heme iron.
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Maskiewicz R, Bielski BH. Kinetics of some electron-transfer reactions in biological photosystems. I. Pulse radiolysis study of spinach ferredoxin reduction by the hydrated electron and CO−2 radical. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1981. [DOI: 10.1016/0005-2728(81)90198-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Van Leeuwen JW, Butler J, Swallow AJ. A non-equilibrium state of deoxyhaemoglobin. Temperature-dependence and oxygen binding. BIOCHIMICA ET BIOPHYSICA ACTA 1981; 667:185-96. [PMID: 7213795 DOI: 10.1016/0005-2795(81)90079-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
After reduction of human methaemoglobin by solvated electrons a non-equilibrium low-spin state of deoxyhaemoglobin is formed which has the characteristic haemochrome spectrum. This haemochrome state is ascribed to a weakly 6-coordinated structure of the haem, which is stabilised by the protonated distal histidine. Oxygen binding is not inhibited by the presence of the weak interaction in the haemochrome state. From the pH dependence of the biphasic behaviour of the oxygen binding a pK of about 8.8 is obtained which is ascribed to the deprotonation of the distal histidine which is in the proximity of a negative ion. A model is proposed to explain the complex spin-equilibria observed in methaemoglobin. The enthalpy of activation of the decay of the haemochrome state is about 53 kJ x mol(-1) and increases to 90 kJ x mol(-1) in the presence of 1 M methanol, indicating a strong interaction between methanol and haemoglobin. Around pH 8.4 the rate constant of the binding of oxygen to the haemochrome state is so high that it may well be diffusion controlled.
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