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Understanding Heme Proteins: Characteristics, Function, and Regulation in Oxygen Transport

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Heme proteins, including hemoglobin and myoglobin, are crucial for oxygen transport and storage in humans. The heme group consists of protoporphyrin IX and ferrous iron (Fe2+), enabling the reversible binding of oxygen. Hemoglobin exists in two forms, T (tense) and R (relaxed), with differences in oxygen affinity influenced by factors such as the Bohr effect and 2,3-bisphosphoglycerate (2,3-BPG). The latter decreases hemoglobin's oxygen affinity, facilitating oxygen release in tissues by binding to deoxyhemoglobin, making these proteins essential for respiratory function.

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Understanding Heme Proteins: Characteristics, Function, and Regulation in Oxygen Transport

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  1. HB Dr. Nasim

  2. Hemeproteins are a group of specialized proteins that contain heme as a tightly bound prosthetic group • hemoglobin and myoglobin, the two most abundant hemeproteins in humans, the heme group serves to reversibly bind oxygen.

  3. Structure of heme • Heme is a complex of protoporphyrin IX and ferrous iron (Fe2+). • The iron is held in the center of the heme molecule by bonds to the four nitrogens of the porphyrin ring. • The heme Fe2+ can form two additional bonds, one on each side of the planar porphyrin ring. • In myoglobin and hemoglobin, one of these positions is coordinated to the side chain of a histidine residue of the globin molecule, whereas the other position is available to bind oxygen

  4. Hemoglobin is found exclusively in red blood cells

  5. Difference B/W T & R forms

  6. Diff B/W Myoglobin and HB Curves

  7. Bohr effect

  8. Bohr effect • an increase in protons (or a lower pO2) shifts the equilibrium to the right (favoring deoxyhemoglobin), whereas an increase in pO2 (or a decrease in protons) shifts the equilibrium to the left.

  9. Bisphosphoglycerate (2,3-BPG) • Bisphosphoglycerate (2,3-BPG) is an important regulator of the binding of oxygen to hemoglobin. • It is the most abundant organic phosphate in the red blood cell, where its concentration is approximately that of hemoglobin. • 2,3-BPG is synthesized from an intermediate of the glycolytic pathway

  10. Function of 2, 3 BPG • 2,3-BPG decreases the oxygen affinity of hemoglobin by binding to deoxyhemoglobin but not to oxyhemoglobin. • Thus helps in unloading of HB

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