Except through loss of blood, the level of iron in humans is fairly constant. On
ID: 486663 • Letter: E
Question
Except through loss of blood, the level of iron in humans is fairly constant. One way iron is moved throughout the body is within a protein molecule known as transferring. An example of the binding mode of the iron in the protein molecule is given below. What is the coordination number of iron in the transferring molecule? Would this be a high spin or low spin iron complex? Explain you answer. Would this iron complex expected to be labile or inert with respect to other metals? Explain. Which specific amino acid residues are used in the binding of iron in transferring? Indicate the oxidation state of iron in the protein molecule given above.Explanation / Answer
a) Coordination number is the number of ligands to which the central metal atom is attached, in the above diagram the central iron atom is attached to 6 donor atom hence the coordination number of Iron is 6
b) high-spin Fe(III) found in ferritin.Iron with +3 oxidation state contains five unpaired electron, due to weak field ligand pairing of electron does not take place making iron high spin in its +3 oxidation state
c) Binding constant for Iron in ferritin K1 = 22.8 and K2 = 21.5 which is much higher when compared to any other metals, so Ferritin forms inert complex with respect to other metal atoms
d) according to structure proposed during 1988 the amino acid residues attahed to Iron are N124 C456 Arginine, N249 C585 Histidine, N95 C426 Tyrosine, N188 C517 Tyrosine and N63 C326 Aspartic acid
e) Transferrin contains two specific high-affinity Fe(III) binding sites. hence oxidation state of iron in transferrin is +3
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