Hemoglobin is found exclusively in red blood cells (RBCs), where its main function is to transport oxygen (O2) from the lungs to the capillaries of the tissues. Hemoglobin A, the major hemoglobin in adults, is composed of four polypeptide chains held together by noncovalent interactions.Each subunit has stretches of a helical structure, and a heme-binding pocket similar to that described for myoglobin. However, the tetrameric hemoglobin molecule is structurally and functionally more complex than myoglobin. For example, hemoglobin
can transport H+ and CO2 from the tissues to the lungs, and can carry four molecules of O2 from the lungs to the cells of the body. Furthermore, the oxygen-binding properties of hemoglobin are regulated by interaction with allosteric effectors.
can transport H+ and CO2 from the tissues to the lungs, and can carry four molecules of O2 from the lungs to the cells of the body. Furthermore, the oxygen-binding properties of hemoglobin are regulated by interaction with allosteric effectors.
Quaternary structure of hemoglobin: The hemoglobin tetramer can be envisioned as being composed of two identical dimmers in which the numbers refer to dimers one and
two.
T form: The deoxy form of hemoglobin is called the “T,” or taut (tense) form. In the T form, the two รกรข dimers interact through a network of ionic bonds and hydrogen bonds that constrain the movement of the polypeptide chains.
R form: The binding of oxygen to hemoglobin causes the rupture of some of the ionic bonds and hydrogen bonds between the dimmers.
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