Structure and function of hemocyanin and Hemethrine.

1. PRESENTATION ON
Hemocyanin
&
Hemethrine PRESENTED BY
SANDEEP KUMAR

2. CONTENTS
 INTRODUCTION
 HAEMERYTHRIN (Hr):-
• STRUCTURE
> DEOXYHEMERYTHRIN
> OXYHEMERYTHRIN
• FUNCTION
 HAEMOCYANINS (Hc) :-
• STRUCTURE
> OXYHAEMOCYANINS
> DIOXYHAEMOCYANINS
• FUNCTION
 CONCLUSION
 REFERENCE

3. INTRODUCTION:-
The commonmode of molecular oxygen with transition metal complexes is oxidation
(i.e., extraction of electrons from the metal or from its ligand). Under appropriate
circumstances the dioxygen molecule may, instead become a ligand. Such reactions are
termed oxygenation, because the dioxygen ligand retains its identity, where as oxidation
reactions are those in which the O2 molecule loses its identity through reduction.
Oxygenation reactions are reversible ie., upon increasing temperature and/or reducing the
partial pressure of O2 the dioxygen ligand is lost by dissociation or by the transfer to another
acceptor (which may be oxidized). The process of reversible oxygenationplays an essential
role in life processes.
In humanbeings or other higher animals there are three known transport and storage
systems, and all employ metalloproteins.The dioxygen(O2) carriers are:–
(1) Hemoglobinand Myoglobin
(2) Hemerythrins (Hr)
(3) Hemocyanin (He)

4. HEAMERYTHRINS (Hr):-
 In invertebrate animals oxygen carrying proteins are often non-hemepigments,
hemerythrin and hemocyanin in place of the familiar hemoglobin.
 Both hemoglobin and hemerythrin have iron as the oxygen carrying metal.
 hemerythrin (as well as hemocyanin), it does not contain a heme group.
 Hemerythrin combines with molecular oxygen in a ratio 2Fe: O2 rather than Fe: O2 found in
hemoglobin.
 In spite of these differences both hemerythrin and hemoglobin function
effectivelyas oxygen carriers.
 Hemerythrin is found in four different invertebrate phyla : sipunculids,
poly-chaetes, priapulids and bachiopods.
,

5. STRUCTURE:- Active site structure of
. Deoxyhemerythrin
• Each monomericunit contains an active site which has two high spin ferrous ions [Fe(II)].
• The ferrous ions are bridged together by a hydroxyl group and two carboxyl groups from an
aspartate residue and a glutamate residue of the protein chain.
• One of the ferrous is hexacoordinated with an octahedral geometry and the other is
pentacoordinated with a distorted trigonal bipyramidal geometry.
• The remaining coordinationsites of hexacoordinatedferrous
and pentacoordinated ferrous are satisfiedby three and two
imidazole nitrogens respectively from histidineresidues of
the protein chain.
• The hydroxyl group serves as a bridging ligand but also functions as
a proton donor to the O2 substrate.

6.  One monomeric unit of hemerythrinbinds one dioxygen.
 The dioxygen adds only to the coordinatively unsaturated ferrous.
 The dioxygen adds to hemerythrinin an oxidative manner resulting in the formation of two
Fe(III) centers and peroxide (O2
2-).
 The oxidative addition is followedby the shifting of proton from the bridged OH to the bound
peroxide resulting in the formation of hydroperoxo (HO2-) group.
 This proton-transfer result in the formationof a singleoxygen
atom (μ-oxo) bridge in oxyhemerythrin.
 The hydroperoxo group is hydrogen bonded
with the μ-oxo group.
Active site structure of Oxyhaemerythrine

7. Binding of Dioxygen (O2) :-
 H

8. Functions:-
 Hemerythrin is a nonheme, dioxygen binding pigment.
 Hemerythrin contains iron (II) which binds oxygen reversibly.
 There is an octameric form with molecular weight of about 108,000 that transports dioxygen
in the blood.
 There are lower molecular weight monomers, dimers, trimers or tetramers.
 Homerythrin consists of eight subunits very much similar in quaternary structure to
myohemerythrin.
 A major difference between the hemoglobins and hemerythrins is in the binding of dioxygen.
 The Oxyhaemerythrin & Deoxyhemerythrin may be oxidised to Fe(lll) space.
 Oxyhaemerythrin is dymagnetic to so the spin coupling or the electron on the to Fe(ll).

9. HAEMOCYANINS :-
 Hemocyaninis another copper containing pigment which contains neither
the heme group nor the cyanide ion.
 The name simply means “blueblood” (Hemo- comes from the Greek haîma,
meaning “blood)
 Hemocyanins are found in many species in the molluscs (eg. Octopus,
snails, squids) and arthropods (eg. Scorpions, crabs, lobsters).
 The copper is in the (+1) oxidation state in the deoxy form and
(+2) in the oxy form.
 Hemocyanin has a molecular weight of 825,000 ,the monomer
is constitutedof 12 subunits of 34,400 molecular weight.

10. STRUCTURE :- Active site structure of
. Deoxyhaemocyanins
 Each monomer contains two cuprous ions [Cu(I)] that reversibly bind
one dioxygen.
 An empty cavity is present between the two cuprous ions to
accommodate the dioxygen.
 The Cu(I)- Cu(I) bond distance is 460 pm (no direct interaction
between them).
 The coordination number of each Cu(I) is three and is satisfied
by three histidines residues from the protein.
 This results in a distorted trigonal pyramidal geometry.
 Two phenylalanine residues which are in close proximity to the
histidines residues provide a hydrophobic environment at the
active site .

11. Active site structure of
. Oxyhaemocyanins :-
 Coordination number of copper changes to five from three.
 Geometry of copper changes to square pyramidal from trigonal pyramidal.
The equatorial plane has two histidyl imidazole nitrogens, the bound oxygens
and the third histidyl nitrogen is axially coordinated to copper.
 The Cu-Cu distance decreases to 360 pm.
 To accommodate the bindingof O2, the protein adjusts its
conformation to bring the two Cu atoms closer together.
 The O2-binding site is formulated as Cu(II)—[O2]2-
—Cu(II)
 Coordination of O2 occurs between the two Cu atoms in
a bridgingdihapto manner .

12. Binding of Dioxygen(O2):-
 Cu(I) is oxidizedto Cu(II).
 O2 is reduced to peroxide O22-.
 The binding and release of O2 correspond
to a two-electron reaction:
 Oxidative addition of dioxygen occurs,
i.e. electron transfer accompanies O2 binding.

13.  Hemocyanins are very large dioxygen transporting proteins that functionin the
hemolymph of invertebrates belonging to several species of the phyla of
Molluscaand Arthropoda.
 These occur as highly cooperative multi-subunits:
 Molluscan hemocyanins consist of 10 or 20 subunits with each functional unit
having a molecular weight of about 55,000 Da.
 Arthropodal hemocyanins are hexamers or multihexamers with large subunits (-
75,000 Dal.
 The deoxy forms of hemocyanins are colourless as a result of their 3d¹⁰ dicopper
(1) centers.
 Binding of O2 leads to intenselyblue oxyhemocyanin.
Function:-

14. REFERENCE:-
 Book — Bioinorganicchemistry
Writer — K.Hussain Reddy
 Book — Inorganic chemistry
Writer — J.D.Lee .

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