L4_Dioxygen molecules.pdf - Dioxygen molecules Uptake...

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Dioxygen molecules: Uptake, transport and storage in hemeglobin and myoglobin
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Before dioxygen can be metabolized, it has to be taken up (reversibly) from the atmosphere and transported to oxygen-depleted Assue where it must be stored unAl actual use. Different organisms have their own strategies to coordinate the dioxygen. Hemerythrins – used for dioxygen transport by certain marine invertebrates, ligate iron through protein side chain ligand atoms only.
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Hemocyanins – copper containing oxygen transport metalloproteins found in antraphods and molluscks, coordinate Cu through S and N amino acid side chain ligand of the surrounding protein. Neither hemocyanin nor hemeryhtrin contain the porphyrin ligand heme system of Mb and Hb. The higher breathing organism use the heme system i.e. monoiron complexes of a certain porphyrin macrocycle, protoporpyhrin IX.
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The corresponding protein are the tetramer hemoglobin (Hb, O 2 uptake in the lungs and transport into blood stream). And monomer myoglobin (Mb, O 2 storage and transport within muscle Assue). At this point, the role of Fe should be specified. Since dioxygen transport is not a catalyAc but a stoichiometric funcAon, about 65% Fe present in a human body is confined to the transport protein Hb alone.
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The content of the oxygen-storage protein myoglobin is roughly 6%. The share of O 2 in air is only about 21% vol and a sufficient level has to be maintained in the Assue even under unfavourable circumstances e.g. above 2000m sea level. Human blood has an approximately 30 Ames higher ‘ solubility for O 2 than water. Solubility in water 6.6ml/L or 3 x 10 -4 M Solubility in blood 200mL/L or 9 x 10 -3 M
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Heme Proteins Iron is certainly the most widespread of the transiAon metals in living system. Its compound parAcipate in a variety of acAviAes. Two main funcAon of iron containing materials are: Transport oxygen MediaAon in electron transfer chains.
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Therefore, so much Fe is required for these purposes – chemical system to store and transport Fe. The compound which the iron is present as heme, the porphyrin complex:
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Structure of protoporphyrin IX.
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Structure of the heme prosthe4c group, protoporphyrin IX plus iron.
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The heme funcAon in all cases in inAmate associaAon with a protein molecule. The chief heme proteins are: 1. Hemoglobins 2. Myoglobins 3. Cytochromes including specila type P-450 4. Enzymes such as catalase and peroxidase
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  • Spring '19
  • jane doe
  • Hemoglobin

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