How do dioxygen binding proteins react with oxygen
they undergo a reversible reaction
Protein + O2 <=> [Protein-O2]
at ambient temperature and partial pressures of O2 equilibrium lies to the far right Products»Reactants
Why s O2 so important?
Both Vertebrates and invertebrates derive most of their energy from “combustion” of organic compounds, which requires large amounts O2,
EG. carbohydrate + O2 -> CO2 +H2O
Why can’t organisms just source oxygen by diffusion through their surface
- For most higher organisms, their S;V ratio at ambient temperature and partial pressures would result in internal O2 concentrations that are insufficient for life
- In response to various stresses, organs and tissues sometimes require rapid infusion of O2, something that wouldn’t be possible with simple diffusion
higher organisms have two important mechanisms for the supply and distribution of this molecule.
1) A circulatory system that actively delivers O2 to all cells
2) Oxygen carrying molecules that overcome the low solubility of O2 in water
O2 carrying proteins: general/intro
- all contain either iron or copper at their active sites
- Haem proteins (iron) all animals and other species
blood: oxy/de-o red/purple - Dicopper- Molluscs and anthropods(lobster/squid)- d/o - blue/colourless
- Diiron proteins- marine worms -o/d violet/colourless
What is the redox chemistry of O2?
Picture
What are the most common haem based proteins?
1) Haemoglobin (Hb) -circulates through the body within red blood cells
2)Myoglobin (Mb) -occurs in the muscle tissue as oxygen carrier proteins,
Both contain at least one haem unit
which is responsible for binding dioxygen to these proteins
What is a haem unit?
-An iron chelate of a tetrapyrrole macrocycle
-occurs in the structure of all Hb’s and Mb’s
-Approximately planar, very rigid and highly conjugated
-electronic transitions between pi and pi* give a characteristic and intense absorption spectrum
(and gives blood its intense colour)
-both Fe(II) and Fe(III) available
