M-CSA Mechanism and Catalytic Site Atlas

Cytochrome-c oxidase (AA3 type)

Cytochrome c oxidase is the component of the respiratory chain that catalyzes the reduction of oxygen to water. Subunits 1-3 form the functional core of the enzyme complex. CO I is the catalytic subunit of the enzyme. Electrons originating in cytochrome c are transferred via the copper A center of subunit 2 and heme A of subunit 1 to the bimetallic center formed by heme A3 and copper B.

Reference Protein and Structure

Sequences: P00396 (7.1.1.9)
P68530 (7.1.1.9)
Q6JTG5 (Sequence Homologues) (PDB Homologues)
Biological species: Bos taurus (Cattle)
PDB: 1v54 - Bovine heart cytochrome c oxidase at the fully oxidized state (1.8 Å)
Catalytic CATH Domains: 1.20.210.10 (see all for 1v54)
Cofactors: Ferroheme a(2-) (2), Copper(2+) (1), Binuclear copper ion (1), Water (15) Metal MACiE

Click To Show Structure

Enzyme Reaction (EC:1.9.3.1)

dioxygen

CHEBI:15379

hydron

CHEBI:15378

iron(2+)

CHEBI:29033

→

water

CHEBI:15377

iron(3+)

CHEBI:29034

Enzyme reaction links: IntEnz ENZYME ExplorEnz

Alternative enzyme names: NADH cytochrome c oxidase, Warburg's respiratory enzyme, Complex IV (mitochondrial electron transport), Cytochrome a3, Cytochrome aa3, Cytochrome oxidase, Ferrocytochrome c oxidase, Indophenol oxidase, Indophenolase,

Enzyme Mechanism

Mechanism Proposal 1 ☆☆☆

Summary
Step 1
Step 2
Step 3
Step 4
Step 5
Step 6
Step 7
Step 8
Step 9
Step 10
Step 11
Step 12
Products
All Steps

Introduction

Cytochrome c oxidase is a redox driven proton pump that utilises free energy of oxygen reduction for creation of proton gradient across the mitochondrial membrane. All protons pumped across the membrane and three out of the four substrate protons consumed per cycle are transferred through the so-called D-pathway. It leads from the conserved Asp91 under involvement of solvent molecules straight up to Ser156 and Ser157 and from there through a large presumably water-filled cavity to the conserved Glu242 [PMID:15147881, PMID:2765763, PMID:9788998]. The further pathway for protons consist of two chain of water molecules. One connecting Glu242 to propionate D of haem A3 via the NH group of Trp126 and one connecting Glu242 to the catalytic site of the enzyme [PMID:15147881, PMID:2765763]. One of the chemical protons presumably comes via the K-pathway. This involves Lys319 that could receive protons either from Ser255 directly or from the conserved subunit II Glu residue indirectly. It would transfer the proton via Thr316 the hydroxy group of the side chain of hame A3 to Tyr244 which is covalently cross-linked to His240 [PMID:15147881, PMID:9788998]. The effect of the cross-link would be to lower the pKa of Tyr244 making this residue a possible proton donor for O2 intermediates bound at the active site [PMID:15598510]. Electrons are supplied by cytochrome c via CuA - haem A - haem A3/CuB at the binuclear centre and the residues Arg438 Arg439 and Phe377 may be involved in these electron transfers [PMID:10775261].

Catalytic Residues Roles

UniProt	PDB* (1v54)
His61	His61A	Heme A axial ligand.	metal ligand
His240, His291, His290	His240A, His291A, His290A	Forms Copper B binding site.	covalently attached, radical stabiliser, metal ligand, electrostatic stabiliser
Trp126, Asp91, Ser156, Ser157, Glu242, His291, Arg438	Trp126A, Asp91A, Ser156A, Ser157A, Glu242A, His291A, Arg438A	Forms a proton relay that is responsible for modulating the protonataion state of His291 via water, Arg438, Trp126, 10 water molecules, Glu242, Ser157, Ser156 and Asp91.	proton relay, proton acceptor, proton donor
Asp91, Ser156, Ser157, Glu242, Tyr244, His291, Ser255, Arg438, Thr316, Lys319	Asp91A, Ser156A, Ser157A, Glu242A, Tyr244A, His291A, Ser255A, Arg438A, Thr316A, Lys319A	General acid/base.	proton relay, proton acceptor, proton donor
Tyr244, Ser255, Thr316, Lys319	Tyr244A, Ser255A, Thr316A, Lys319A	Forms the proton relay chain that helps modulate the protonation state of Tyr244. Bulk water is deprotonated through a proton relay chain that involves 2 water molecules, Thr316, Lys319 and Ser255.	hydrogen radical donor, covalently attached, proton acceptor, proton donor, proton relay, single electron acceptor

*PDB label guide - RESx(y)B(C) - RES: Residue Name; x: Residue ID in PDB file; y: Residue ID in PDB sequence if different from PDB file; B: PDB Chain; C: Biological Assembly Chain if different from PDB. If label is "Not Found" it means this residue is not found in the reference PDB.

Chemical Components

bimolecular nucleophilic addition, redox reaction, hydride transfer, bimolecular nucleophilic substitution, radical formation, overall reactant used, cofactor used, coordination to a metal ion, intermediate formation, proton transfer, proton relay, electron transfer, radical termination, native state of cofactor regenerated, overall product formed, electron relay, intermediate terminated, intermediate collapse, decoordination from a metal ion, native state of enzyme regenerated

References

Popović DM et al. (2004), FEBS Lett, 566, 126-130. Proton pumping mechanism and catalytic cycle of cytochromecoxidase: Coulomb pump model with kinetic gating. DOI:10.1016/j.febslet.2004.04.016. PMID:15147881.
Schaefer AW et al. (2017), J Am Chem Soc, 139, 7958-7973. Phenol-Induced O-O Bond Cleavage in a Low-Spin Heme-Peroxo-Copper Complex: Implications for O₂ Reduction in Heme-Copper Oxidases. DOI:10.1021/jacs.7b03292. PMID:28521498.
Shimada S et al. (2017), EMBO J, 36, 291-300. Complex structure of cytochrome c-cytochrome c oxidase reveals a novel protein-protein interaction mode. DOI:10.15252/embj.201695021. PMID:27979921.
Cassano JA et al. (2016), Photochem Photobiol, 92, 410-419. The CO Photodissociation and Recombination Dynamics of the W172Y/F282T Ligand Channel Mutant of Rhodobacter sphaeroides aa3 Cytochrome c Oxidase. DOI:10.1111/php.12587. PMID:27029379.
Yano N et al. (2016), J Biol Chem, 291, 23882-23894. The Mg2+-containing Water Cluster of Mammalian Cytochrome c Oxidase Collects Four Pumping Proton Equivalents in Each Catalytic Cycle. DOI:10.1074/jbc.M115.711770. PMID:27605664.
Sousa JS et al. (2016), Elife, 5,Functional asymmetry and electron flow in the bovine respirasome. DOI:10.7554/eLife.21290. PMID:27830641.
Ishigami I et al. (2015), Biochim Biophys Acta, 1847, 98-108. Proton translocation in cytochrome c oxidase: insights from proton exchange kinetics and vibrational spectroscopy. DOI:10.1016/j.bbabio.2014.09.008. PMID:25268561.
Goyal P et al. (2015), Chem Sci, 6, 826-841. Microscopic basis for kinetic gating in Cytochrome c oxidase: insights from QM/MM analysis. DOI:10.1039/C4SC01674B. PMID:25678950.
Sharma V et al. (2015), Proc Natl Acad Sci U S A, 112, 2040-2045. Proton-coupled electron transfer and the role of water molecules in proton pumping by cytochrome c oxidase. DOI:10.1073/pnas.1409543112. PMID:25646428.
Vilhjálmsdóttir J et al. (2015), Sci Rep, 5, 12047-. Structural Changes and Proton Transfer in Cytochrome c Oxidase. DOI:10.1038/srep12047. PMID:26310633.
Oliveira AS et al. (2014), PLoS Comput Biol, 10, e1004010-. Exploring O2 diffusion in A-type cytochrome c oxidases: molecular dynamics simulations uncover two alternative channels towards the binuclear site. DOI:10.1371/journal.pcbi.1004010. PMID:25474152.
Lu J et al. (2014), Proc Natl Acad Sci U S A, 111, 12414-12419. Characterizing the proton loading site in cytochrome c oxidase. DOI:10.1073/pnas.1407187111. PMID:25114210.
Sharma V et al. (2013), Proc Natl Acad Sci U S A, 110, 16844-16849. Computational study of the activated O(H) state in the catalytic mechanism of cytochrome c oxidase. DOI:10.1073/pnas.1220379110. PMID:24082138.
McDonald W et al. (2013), Biochemistry, 52, 640-652. Ligand access to the active site in Thermus thermophilus ba(3) and bovine heart aa(3) cytochrome oxidases. DOI:10.1021/bi301358a. PMID:23282175.
Brzezinski P et al. (2013), Biochim Biophys Acta, 1827, 843-847. Intermediates generated during the reaction of reduced Rhodobacter sphaeroides cytochrome c oxidase with dioxygen. DOI:10.1016/j.bbabio.2013.04.007. PMID:23643727.
Egawa T et al. (2013), PLoS One, 8, e63669-. Redox-controlled proton gating in bovine cytochrome c oxidase. DOI:10.1371/journal.pone.0063669. PMID:23696843.
Kubo M et al. (2013), J Biol Chem, 288, 30259-30269. 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. DOI:10.1074/jbc.M113.473983. PMID:23996000.
Johansson AL et al. (2013), Proc Natl Acad Sci U S A, 110, 8912-8917. Role of aspartate 132 at the orifice of a proton pathway in cytochrome c oxidase. DOI:10.1073/pnas.1303954110. PMID:23674679.
Rich PR et al. (2013), J R Soc Interface, 10, 20130183-. Functions of the hydrophilic channels in protonmotive cytochrome c oxidase. DOI:10.1098/rsif.2013.0183. PMID:23864498.
Goyal P et al. (2013), Proc Natl Acad Sci U S A, 110, 18886-18891. Changing hydration level in an internal cavity modulates the proton affinity of a key glutamate in cytochrome c oxidase. DOI:10.1073/pnas.1313908110. PMID:24198332.
Einarsdóttir O et al. (2012), Biochim Biophys Acta, 1817, 672-679. Kinetic studies of the reactions of O(2) and NO with reduced Thermus thermophilus ba(3) and bovine aa(3) using photolabile carriers. DOI:10.1016/j.bbabio.2011.12.005. PMID:22201543.
Szundi I et al. (2012), Biochemistry, 51, 9302-9311. Spectral identification of intermediates generated during the reaction of dioxygen with the wild-type and EQ(I-286) mutant of Rhodobacter sphaeroides cytochrome c oxidase. DOI:10.1021/bi301166u. PMID:23057757.
Konstantinov AA (2012), FEBS Lett, 586, 630-639. Cytochrome c oxidase: Intermediates of the catalytic cycle and their energy-coupled interconversion. DOI:10.1016/j.febslet.2011.08.037. PMID:21889506.
Popović DM et al. (2012), Biochim Biophys Acta, 1817, 506-517. Coupled electron and proton transfer reactions during the O→E transition in bovine cytochrome c oxidase. DOI:10.1016/j.bbabio.2011.10.013. PMID:22086149.
Johansson AL et al. (2011), Biochim Biophys Acta, 1807, 1083-1094. Proton-transport mechanisms in cytochrome c oxidase revealed by studies of kinetic isotope effects. DOI:10.1016/j.bbabio.2011.03.012. PMID:21463601.
Kaila VR et al. (2011), Biochim Biophys Acta, 1807, 769-778. A combined quantum chemical and crystallographic study on the oxidized binuclear center of cytochrome c oxidase. DOI:10.1016/j.bbabio.2010.12.016. PMID:21211513.
Lee HJ et al. (2010), J Am Chem Soc, 132, 16225-16239. Intricate role of water in proton transport through cytochrome c oxidase. DOI:10.1021/ja107244g. PMID:20964330.
Ohta K et al. (2010), Acta Crystallogr Sect F Struct Biol Cryst Commun, 66, 251-253. X-ray structure of the NO-bound Cu(B) in bovine cytochrome c oxidase. DOI:10.1107/S1744309109055109. PMID:20208153.
Muramoto K et al. (2010), Proc Natl Acad Sci U S A, 107, 7740-7745. Bovine cytochrome c oxidase structures enable O2 reduction with minimization of reactive oxygens and provide a proton-pumping gate. DOI:10.1073/pnas.0910410107. PMID:20385840.
Lee HJ et al. (2009), Biochemistry, 48, 7123-7131. Properties of Arg481 mutants of the aa3-type cytochrome c oxidase from Rhodobacter sphaeroides suggest that neither R481 nor the nearby D-propionate of heme a3 is likely to be the proton loading site of the proton pump. DOI:10.1021/bi901015d. PMID:19575527.
Aoyama H et al. (2009), Proc Natl Acad Sci U S A, 106, 2165-2169. A peroxide bridge between Fe and Cu ions in the O2 reduction site of fully oxidized cytochrome c oxidase could suppress the proton pump. DOI:10.1073/pnas.0806391106. PMID:19164527.
Muramoto K et al. (2007), Proc Natl Acad Sci U S A, 104, 7881-7886. A histidine residue acting as a controlling site for dioxygen reduction and proton pumping by cytochrome c oxidase. DOI:10.1073/pnas.0610031104. PMID:17470809.
Brunori M et al. (2005), J Inorg Biochem, 99, 324-336. Cytochrome oxidase, ligands and electrons. DOI:10.1016/j.jinorgbio.2004.10.011. PMID:15598510.
Namslauer A et al. (2004), FEBS Lett, 567, 103-110. Structural elements involved in electron-coupled proton transfer in cytochromecoxidase. DOI:10.1016/j.febslet.2004.04.027. PMID:15165901.
Wikström M et al. (2003), Biochim Biophys Acta, 1604, 61-65. Water-gated mechanism of proton translocation by cytochrome c oxidase. DOI:10.1016/s0005-2728(03)00041-0. PMID:12765763.
Tsukihara T et al. (2003), Proc Natl Acad Sci U S A, 100, 15304-15309. The low-spin heme of cytochrome c oxidase as the driving element of the proton-pumping process. DOI:10.1073/pnas.2635097100. PMID:14673090.
Soulimane T et al. (2000), EMBO J, 19, 1766-1776. Structure and mechanism of the aberrant ba3-cytochrome c oxidase from Thermus thermophilus. DOI:10.1093/emboj/19.8.1766. PMID:10775261.
Fei MJ et al. (2000), Acta Crystallogr D Biol Crystallogr, 56, 529-535. X-ray structure of azide-bound fully oxidized cytochrome c oxidase from bovine heart at 2.9 A resolution. PMID:10771420.
Buse G et al. (1999), Protein Sci, 8, 985-990. Evidence for a copper-coordinated histidine-tyrosine cross-link in the active site of cytochrome oxidase. DOI:10.1110/ps.8.5.985. PMID:10338009.
Michel H (1998), Proc Natl Acad Sci U S A, 95, 12819-12824. The mechanism of proton pumping by cytochrome c oxidasex127e [comments]. PMID:9788998.
Hofacker I et al. (1998), Proteins, 30, 100-107. Oxygen and proton pathways in cytochrome c oxidase. DOI:10.1002/(sici)1097-0134(199801)30:1<100::aid-prot9>3.3.co;2-q. PMID:9443344.

Step 1. Dioxygen initiates a electrophilic attack on Fe(II).

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Catalytic Residues Roles

Residue	Roles
His240A	covalently attached
Tyr244A	covalently attached
His240A	electrostatic stabiliser
His240A	metal ligand
His291A	metal ligand
His61A	metal ligand
His290A	metal ligand

Chemical Components

ingold: bimolecular nucleophilic addition, redox reaction, hydride transfer, ingold: bimolecular nucleophilic substitution, radical formation, overall reactant used, cofactor used, coordination to a metal ion, intermediate formation

Step 2. Dioxygen transfers two electrons to Fe(II). Through a series of homolytic reactions, the copper centre then transfers a single electron to Tyr244, and the dioxygen bond is cleaved. The net result is Fe(IV) with a oxo group bound,a tyrosyl radical and Cu(II) with a hydroxide group bound.

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Catalytic Residues Roles

Residue	Roles
His240A	covalently attached
Tyr244A	covalently attached
His240A	electrostatic stabiliser
His240A	metal ligand
His291A	metal ligand
His61A	metal ligand
His290A	metal ligand
Tyr244A	hydrogen radical donor

Chemical Components

Step 3. Water deprotonates His291. The Cu(II) bound hydroxide deprotonates bulk water through a proton relay chain that includes 11 water molecules, Glu242, Ser157, Ser156 and Asp91.

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Catalytic Residues Roles

Residue	Roles
His240A	covalently attached
Tyr244A	covalently attached
His240A	radical stabiliser, metal ligand
His291A	metal ligand
His61A	metal ligand
His290A	metal ligand
Glu242A	proton acceptor
Ser157A	proton donor
Ser156A	proton donor
Asp91A	proton donor
His291A	proton donor
Asp91A	proton relay
Ser156A	proton relay
Ser157A	proton relay
Asp91A	proton acceptor
Ser156A	proton acceptor
Ser157A	proton acceptor
Glu242A	proton donor, proton relay

Chemical Components

proton transfer, intermediate formation, proton relay

Step 4. A single electron is transferred from ferrocytochrome C, to CuA, Haem A to Haem A3 and thence to Cu(II), which immediately donates its electron to the tyrosyl radical. His291 deprotonates water, which deprotonates Arg438, thence Trp126 which deprotonates bulk water through a proton relay chain that includes 10 water molecules, Glu242, Ser157, Ser156 and Asp91.

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Catalytic Residues Roles

Residue	Roles
His240A	metal ligand
His291A	metal ligand
His61A	metal ligand
His290A	metal ligand
His240A	radical stabiliser, covalently attached
Tyr244A	covalently attached
Trp126A	proton acceptor
Asp91A	proton acceptor
Arg438A	proton donor
His291A	proton acceptor
Asp91A	proton donor
Ser156A	proton donor
Glu242A	proton acceptor
Trp126A	proton donor
Asp91A	proton relay
Trp126A	proton relay
Ser156A	proton relay
Ser157A	proton relay
Glu242A	proton relay
Arg438A	proton relay
Tyr244A	single electron acceptor
Arg438A	proton acceptor
Ser156A	proton acceptor
Ser157A	proton acceptor, proton donor
Glu242A	proton donor

Chemical Components

proton transfer, electron transfer, radical termination, overall reactant used, cofactor used, native state of cofactor regenerated, overall product formed, proton relay, electron relay

Step 5. Tyr244 deprotonates Cu(II) bound water.

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Catalytic Residues Roles

Residue	Roles
His240A	metal ligand
His291A	metal ligand
His61A	metal ligand
His290A	metal ligand
His240A	covalently attached
Tyr244A	covalently attached
His240A	electrostatic stabiliser
Tyr244A	proton acceptor

Chemical Components

proton transfer, intermediate formation

Step 6. Water deprotonates His291. The Cu(II) bound hydroxide deprotonates bulk water through a proton relay chain that includes 11 water molecules, Glu242, Ser157, Ser156 and Asp91.

Download: Image, Marvin File

Catalytic Residues Roles

Residue	Roles
His240A	metal ligand
His291A	metal ligand
His61A	metal ligand
His290A	metal ligand
His240A	covalently attached
Tyr244A	covalently attached
His240A	electrostatic stabiliser
Glu242A	proton donor
Asp91A	proton acceptor
Ser156A	proton acceptor
Asp91A	proton relay
Ser156A	proton relay
Ser157A	proton relay
Glu242A	proton relay
Ser157A	proton donor
Glu242A	proton acceptor
Ser157A	proton acceptor
Ser156A	proton donor
Asp91A	proton donor
His291A	proton donor

Chemical Components

proton transfer, intermediate formation, proton relay

Step 7. A single electron is transferred from ferrocytochrome C, to CuA, Haem A to Haem A3 and thence to Cu(II). His291 deprotonates water, which deprotonates Arg438, thence Trp126 which deprotonates bulk water through a proton relay chain that includes 10 water molecules, Glu242, Ser157, Ser156 and Asp91.

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Catalytic Residues Roles

Residue	Roles
His240A	metal ligand
His291A	metal ligand
His61A	metal ligand
His290A	metal ligand
Asp91A	proton relay
Trp126A	proton relay, proton donor, proton acceptor
Arg438A	proton acceptor
His291A	proton acceptor
Asp91A	proton acceptor, proton donor
Ser156A	proton acceptor, proton donor
Ser157A	proton acceptor, proton donor
Glu242A	proton acceptor, proton donor
Arg438A	proton donor
Ser156A	proton relay
Ser157A	proton relay
Glu242A	proton relay
Arg438A	proton relay

Chemical Components

proton transfer, electron transfer, overall reactant used, cofactor used, native state of cofactor regenerated, intermediate formation, overall product formed, proton relay, electron relay

Step 8. Cu(I) donates a single electron to Fe(IV), which causes the oxo group to deprotonate the Cu(I) bound water.

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Catalytic Residues Roles

Residue	Roles
His240A	covalently attached
Tyr244A	covalently attached
His240A	electrostatic stabiliser
His240A	metal ligand
His291A	metal ligand
His61A	metal ligand
His290A	metal ligand

Chemical Components

proton transfer, electron transfer, intermediate formation

Step 9. Water deprotonates His291. The Fe(III) bound hydroxide deprotonates bulk water through a proton relay chain that includes 11 water molecules, Glu242, Ser157, Ser156 and Asp91.

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Catalytic Residues Roles

Residue	Roles
His240A	covalently attached
Tyr244A	covalently attached
His240A	electrostatic stabiliser, metal ligand
His291A	metal ligand
His61A	metal ligand
His290A	metal ligand
Asp91A	proton acceptor
Ser156A	proton acceptor
His291A	proton donor
Asp91A	proton donor
Glu242A	proton donor
Ser156A	proton donor
Ser157A	proton acceptor, proton donor
Glu242A	proton acceptor
Asp91A	proton relay
Ser156A	proton relay
Ser157A	proton relay
Glu242A	proton relay

Chemical Components

proton transfer, intermediate formation, proton relay

Step 10. A single electron is transferred from ferrocytochrome C, to CuA, Haem A to the Fe(III) of Haem A3, which causes the elimination of the Fe(II) bound water molecule. The carboxylate of Haem A3 deprotonates Trp126, which deprotonates bulk water through a proton relay chain that includes 10 water molecules, Glu242, Ser157, Ser156 and Asp91.

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Catalytic Residues Roles

Residue	Roles
His240A	metal ligand
His291A	metal ligand
His61A	metal ligand
His290A	metal ligand
Glu242A	proton acceptor
Ser157A	proton acceptor
Ser156A	proton acceptor
Asp91A	proton acceptor
Arg438A	proton donor
Trp126A	proton acceptor
Glu242A	proton donor
Arg438A	proton acceptor
Asp91A	proton donor
Ser157A	proton donor
Ser156A	proton donor
Trp126A	proton donor
His291A	proton acceptor
Asp91A	proton relay
Trp126A	proton relay
Ser156A	proton relay
Ser157A	proton relay
Glu242A	proton relay
Arg438A	proton relay

Chemical Components

proton transfer, electron transfer, overall reactant used, cofactor used, native state of cofactor regenerated, intermediate terminated, intermediate collapse, decoordination from a metal ion, overall product formed, proton relay, electron relay

Step 11. Water deprotonates His291. The Cu(II) bound hydroxide deprotonates Tyr244, which deprotonates the hydroxyl group of Haem A3, which deprotonates bulk water through a proton relay chain that involves 2 water molecules, Thr316, Lys319 and Ser255.

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Catalytic Residues Roles

Residue	Roles
His240A	metal ligand
His291A	metal ligand
His61A	metal ligand
His290A	metal ligand
His240A	covalently attached
Tyr244A	covalently attached
His240A	electrostatic stabiliser
Ser255A	proton acceptor
Thr316A	proton donor, proton acceptor
Lys319A	proton donor, proton acceptor
Ser255A	proton donor
Tyr244A	proton donor
His291A	proton donor
Tyr244A	proton acceptor, proton relay
Ser255A	proton relay
Thr316A	proton relay
Lys319A	proton relay

Chemical Components

proton transfer, cofactor used, native state of cofactor regenerated, intermediate formation, proton relay

Step 12. A single electron is transferred from ferrocytochrome C, to CuA, Haem A to Haem A3 and thence to Cu(II). His291 deprotonates water, which deprotonates Arg438, thence Trp126 which deprotonates bulk water through a proton relay chain that includes 10 water molecules, Glu242, Ser157, Ser156 and Asp91.

Download: Image, Marvin File

Catalytic Residues Roles

Residue	Roles
His240A	metal ligand
His291A	metal ligand
His61A	metal ligand
His290A	metal ligand
His240A	covalently attached
Tyr244A	covalently attached
His240A	electrostatic stabiliser
Trp126A	proton acceptor
Glu242A	proton acceptor
Ser157A	proton donor
Arg438A	proton donor
Trp126A	proton donor
Ser156A	proton donor
Ser157A	proton acceptor
Glu242A	proton donor
Ser156A	proton acceptor
Asp91A	proton acceptor, proton donor
Arg438A	proton acceptor
His291A	proton acceptor
Asp91A	proton relay
Trp126A	proton relay
Ser156A	proton relay
Ser157A	proton relay
Glu242A	proton relay
Arg438A	proton relay

Chemical Components

proton transfer, electron transfer, overall reactant used, cofactor used, native state of cofactor regenerated, intermediate terminated, overall product formed, proton relay, electron relay, native state of enzyme regenerated

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Step 1. Dioxygen initiates a electrophilic attack on Fe(II).

Step 3. Water deprotonates His291. The Cu(II) bound hydroxide deprotonates bulk water through a proton relay chain that includes 11 water molecules, Glu242, Ser157, Ser156 and Asp91.

Step 5. Tyr244 deprotonates Cu(II) bound water.

Step 6. Water deprotonates His291. The Cu(II) bound hydroxide deprotonates bulk water through a proton relay chain that includes 11 water molecules, Glu242, Ser157, Ser156 and Asp91.

Step 8. Cu(I) donates a single electron to Fe(IV), which causes the oxo group to deprotonate the Cu(I) bound water.

Step 9. Water deprotonates His291. The Fe(III) bound hydroxide deprotonates bulk water through a proton relay chain that includes 11 water molecules, Glu242, Ser157, Ser156 and Asp91.

Products.

Contributors

Gemma L. Holliday, Daniel E. Almonacid