CH3208 Bioinorganic chemistry
Transcript of CH3208 Bioinorganic chemistry
CH3208 Bioinorganic chemistry
Lecture 1
By
Dr. Moumita Mondal
Transport and storage of dioxygen
All the known O2 transport and storage system employ metalloproteins
Dixoygen carrier Hemoglobin (Hb), Hemocyanin (Hc), Hemerythrin (Hr)
The O2 molecules stored in tissues like muscle by myoglobin (Mb) and myohemerythrin
Hb amd Mb are the only heme protein (i. e. these have an iron- porphyrin group), found in human beings and bigger animals Hr is a non-heme protein (although its name carries the term heme) and
this oxygen carrier is found in lower organisms has two non-heme iron atoms in its functional core Hc has two copper atoms.
Ref P. S. Kalsi, J. P. Kalsi, Bioorganic, Bioinorganic and Supramolecular Chemistry
Structure and function of Mb and Hb
heme containing protein (molecular weight ~ 17, 000) and its protein chain consists of a single polypeptide chain of 153 amino acid residues which folds around the heme prosthic group. In both myoglobin and hemoglobin one has heme b-the iron(II) complex of protoporphyrin IX
v
Ref P. S. Kalsi, J. P. Kalsi, Bioorganic, Bioinorganic and Supramolecular Chemistry
Partially buried in hydrophobic
interior
Hydrophobic nature nonpolar side chains of protein ensures reversible oxygen binding by inhibiting permanent oxidation of Fe
Structure of Myoglobin
Structure of Hemoglobin
Deoxy Mb/Hb
Proximal histidine
nitrogen atom (F8)
Fe(II) high spin
Pseudo Oh geometry Tense or T conformational state
Radii of high spin Fe(II) is 92 pm, too large to fit in porphyrin cavity It lies 42 pm above the plane of porphyrin Electron donating coordinated nitrogen atom prevents oxidation of Fe
Ref P. S. Kalsi, J. P. Kalsi, Bioorganic, Bioinorganic and Supramolecular Chemistry
Oxy Mb/Hb
Pseudo Oh geometry Relaled or R conformational state
Fe(III) low spin
Radii of low spin Fe(III) is 75 pm, fits into porphyrin cavity
Overall result is vibration or breathing of protein structure on binding and dissociation of oxygen
Dioxygen is bonded to Fe by end on bent fashion Fe-O-O bond angle 115 o, νO-O 1105 cm-1
HbO2/MbO2 are best represented as Fe(III) coordinated superoxide
Hydrogen bonding
facilitates O2 binding
Vibrational Spectroscopic Evidence that OxyHb and OxyMb are Formally FeIII–O2
- Species
From resonance Raman spectroscopy the O–O stretch in oxyMb is measured to be ~ 1105 cm-1. The protein is also diamagnetic (d5, Fe(III) and O2
- couple).
Reaction of free heme and O2 in aq. Solution
Release of superoxide anion in presence of Nu
Formation of hematin
μ-peroxo complex
ferryl complex
Acid catalysed release of superoxide in presence of water
Met Hb
O2 binding curve for Mb is hyperbolic O2 binding curve for Hb is sigmoidal i. e. positive cooperitivity of binding
At high pO2 Hb and Mb binds
oxygen equally well
At low pO2 Hb is poor binder than
Mb
Transport of dioxygen
Bohr effect carbamyl Hb
Met Hb
Structure and function of Hemerythrin(Hr)
Oxygen binding mechanism of Hr
O2 binds asymmetrically to Hr by end on coordination to only one iron centre
H atom of OH bridge stabilize peroxo ion
Structure and function of Hemocyanin(Hc)
Oxygen binding mechanism of Hc