Hemoerythrine and Hemocyanin

1. Hemerythrin
 Non-heme Fe containing protein found
in invertebrates
 Contain Fe(II) and binds oxygen
reversibly
 Contains 8 subunits with 113
aminoacids and 2 Fe(II) active sites.
 difference b/W Hb and Mb is in the
binding of oxygen
 He does not exhibit cooperativity.
 Each subunit in He consists 2 Fe active sites connected by 3 bridged gps.
 Two of which are carbonyl anions from Glutamate and Aspartate and the other is
either H2O, Oh or o22-, but probably OH.
 Remaing coordinates to N-atom of His residue.
 Deoxy-He are strongly antiferromagnetically coupled through the Fe-O-Fe bridge
 Deoxy-He paramagnetic and High spin.
 Fe atom is pseudo Oh.

2. Hemocyanin
• It suggests the presence of Heme gp and as well as cyanide ion.
• Copper containing protein carries oxygen in invertribartes.
• Deoxy Hc contains Cu(I) ion and is colorless.
• Oxygenation provides Cu with normal coordinated structure and remove a strain.
• Deoxy-Hc is diamagnetic, colorless in which both Cu atom in +1 oxidation state.

3. cytochromes
• Found in both plants and animals and serves as electron carriers.
• Contain heme like prosthetic group
• A prosthetic group is compound required by an enzyme to facilitate a particular reaction, such compounds are also called as
coenzymes.
• The peptide portion of an enzyme that requires a prostetic group is called the Haloenzyme.
• There are three main types of cytochromes
1) Cytochrome a
2) Cytochrome b
3) Cytochrome c
 As in Hb, the Fe(II) ion of heme gp is attached to a N-atom of His.
 6th coordination site is occupied by atightly bound S atom form Methionine of protein.
 For this reason Cyt are inert not only to the oxygen but also CO which affects oxygen carrier.
 The reduction potentials of cyt increases in the order: Cyt-b(0.26v), Cyt-c (026v) and Cyt-a(0.4v).
 Therefore the flow of electrons is in the order: b---- c --- a --- oxygen.
 ETC allows energy from Glucose oxidation to be released gradually and to be stored in the form of ATP.
 Cyt-c-oxidase, the terminal member of the cyt chain, which binds the inner membrane of the mitochondria contains Cyt-a,
Cyt-a3 and two Cu(II) ions (CuA & CuB).
 Electron transfer involves the Cyt-a, CuA

4. • The electron being transported form Cyt-c to CuA and then to Cyt-a.
• The Cyt-a3 and CuB provides site for oxygen binding and conversion of oxygen to
water.
• Cyt-a3 and CuB are 5 and 3 coordinated respectively and therefore binds oxygen.
• Cyt chain not only involves the transfer of electrons but also transport prontos
across the mitochondrial membrane.
• The oxidized form of Cyt a3 is susceptible to bind CN- that renders cyanide toxic.