Dioxygen molecules: Uptake, transport and storage in hemeglobin and myoglobin
• 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.
• 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.
• 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.
• 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
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.
• 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:
Structure of protoporphyrin IX.
Structure of the heme prosthe4c group, protoporphyrin IX plus iron.
• 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
- Spring '19
- jane doe
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