Related to Bioinorganic chemistry: the enzyme known as beta hydroxylase enzymes

1. DOPAMINE-β-HYDROXYLASE
PRESENTED BY:
CHURCHIL SHARMA
BIOINORGANIC CHEMISTRY (ICHT905)
MSc. Chemistry

2. INDEX
 Types of copper centres
 Enzymes containing copper
 Dopamine β- hydroxylase
 Mechanism
 Modelling of the activity of the Cub site of dopamine
β-hydroxylase
 Conclusion

3. In Cu-containing proteins, three types of Cu centres are found,
classified on the basis of their visible, UV, and EPR spectra
TYPE 1 TYPE 2 TYPE 3
Single Cu atom Single Cu atom Di Cu atom
Blue Colourless Colourless
Intense blue optical
absorption band
Weak absorption spectrum
Strong absorption in the
near UV
EPR spectrum with an
uncommonly small
hyperfine splitting
EPR spectrum
characteristic of square-
planar Cu(II) complexes
No EPR spectra, the two
Coppers are
antiferromagnetically
coupled.
Distorted tetrahedral centre
by three strong
Ligands, a cysteine and two
histidines and one weaker
ligand such as methionine
sulfur or a nitrogen or
oxygen donor
Square-planar or tetragonal
geometry around the Cu
with nitrogen or oxygen
Ligands
Coppers are usually each
coordinated by three
histidines, with a bridging
ligand such as oxygen or
Hydroxyl anion.

4. ENZYMES CONTAINING COPPER
Ceruloplasmin (ferroxidase I) (Type 1)
Cytochrome c oxidase ) (Type 1)
Amine oxidases (type 2)
Peptidylglycine alpha-amidating mono-oxygenase (PAM)(type 2)
Superoxide dismutase(Cu, Zn)(type 2)
Tyrosinase (type 3)
Dopamine β-hydroxylase (type 2)
Catechol oxidase(type 3)

5. DOPAMINE β- HYDROXYLASE
• Dopamine β-hydroxylase catalyses the side-chain
hydroxylation of dopamine and other phenylethylamine
derivatives.
• Ascorbic acid serves as a specific electron-donating cofactor.
• When the enzyme oxidizes ascorbate dehydroascorbate , most
of the Cu2+ is reduced to Cu+ .
• Added substrate is hydroxylated, and Cu+ is reoxidized to Cu2+
This indicates that most of the protein-bound Cu2+ undergoes
cyclic reduction and oxidation during hydroxylation

6. Peptidyl-glycine hydroxylating monooxygenase (PMH), which
converts C-terminal glycine extended peptides to their α-
hydroxylated products and dopamine β- hydroxylase (DβH), which
converts dopamine to noradrenaline.
Reference : Biological inorganic chemistry by Robert R. Crichton

8. MECHANISM
• Both enzymes contain two Cu atoms.
• Dioxygen binds to one of the two type 2 Cu in an ‘end-on mode’.
• A copper dioxygen complex has been trapped by freezing crystals of
the enzyme which had been soaked with a slowly reacting substrate,
N-acetyldiiodo-tyrosyl-D-threonine (IYT), in the presence of
oxygen and ascorbate.
• Substrate and O2 bind to the reduced enzyme, triggering initial O2
activation involving electron transfer from the type 2 Cu atom, to
form the Cu super oxo intermediate. A second electron is then
transferred from the other Cu site, followed by-product release and
reduction of the two Cu sites by ascorbate.

9. MODELING OF THE ACTIVITY OF THE CuB
SITE OF DOPAMINE β-HYDROXYLASE
• It contains two inequivalent copper atoms in the active site.
• the catalytic properties of a copper(II) complex
[Cu(salgly)(bpy)].4H2O models the activity of the CuB site of
DBH.
• here salgly is a tridentate Schiff-base ligand obtained from the
condensation of glycine and salicylaldehyde.
• The complex is one-electron paramagnetic giving a magnetic
moment of 1.83 mB (298 K)

10. Reference: Reddy A.N.; Datta R.; Chakravarty A.R.; Synthesis, X-ray structure and catalytic properties of a copper(II)
Schiff base complex modeling the activity of the CuB site of dopamine β- hydroxylase, Inorganic Chemistry
Communications, 2000, 3, 322–324

11. • The copper(I) species is reactive towards PhCH2NH2 in the presence of O2.
• The formation of benzaldehyde from benzylamine is evidenced from the
mass spectral studies showing two peaks at 105.2 (m/z) and 106.4 (m/z)
assignable to PhCO+ and PhCHO, respectively.
• The initial step of the catalytic reaction is the one-electron reduction of
copper along with the concomitant protonation of the salgly ligand by
ascorbate which undergoes oxidation to dehydroascorbic species.
• A copper(II) bound hydroperoxo species [Cu(II)–OOH] formed by oxygen
at the CuB site leads to the hydroxylation of dopamine . It is presumed that
a similar hydroperoxo species with the metal centre bonded to benzylamine
is responsible for the attack of the hydroperoxo moiety on the benzylic
carbon to form α -hydroxyamine which being unstable converts to
benzaldehyde by deamination. The formation of benzaldehyde from a

12. CONCLUSION
• A copper(II) Schiff base complex has been found to be
catalytically active in ascorbate oxidation by molecular oxygen
• The oxidation of benzylamine to benzaldehyde involving the
reduced copper(I) intermediate under aerobic conditions
models the activity of the CuB site of dopamine β-hydroxylase.

13. REFERENCES
• Reddy A.N.; Datta R.; Chakravarty A.R.; Synthesis, X-ray
structure and catalytic properties of a copper(II) Schiff base
complex modelling the activity of the CuB site of dopamine β-
hydroxylase, Inorganic Chemistry Communications, 2000, 3,
322–324
• Crichton R.R.; Biological inorganic chemistry, chapter 7,
copper copying with dioxygen, 279-283

14. Thank You