Lec 15 - Lec 15 Hemoglobin and myoglobin Hemoglobin is...

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Lec 15 Hemoglobin and myoglobin Hemoglobin is tetrameric protein, allows for interactions among the four binding sites. Myoglobin is monomeric protein can bind oxygen reversibly to its heme ion. Myoglobin Useless as carrier, binds very well but hard to get off. Hemoglobin---oxygen binds well in the lungs and releases easily in the tissues. Myoglobin like protein which released oxygen effectively in tissues will not bind in the lungs. Sygmoidal curve is critical. S shaped curve is observed for any ligand that can bind to ferrous ion of hemoglobin. CARBON MONOXIDE, CO, not DIOXIDE is ligand for ferrous ion, binds with sygmoidal curve. The difference is that CO bound 200 greater affinity, that’s why it’s a problem for survival. Bound tightly, so it is Hard to displace it with oxygen. People who are poisoned withcarbon monoxide, have hemoglobin iron occupied with CO. Bohr effect is critical component. Physiologically perfect sense. PH of tissue falls with active metabolism--- encourage hemoglobin to give up it’s oxygen. Effective mechanism for decreasing affinity of hemoglobin for oxygen . pH down—oxygen comes off from protein, and affinity for oxygen is increased as you add oxygen to protein process of binding will be associated with protons bound to protein. Increasing p50 as environment more acidic, associated with carbon dioxide transport in the body. CO2 is not bound to hemoglobin. CO2 reacts with water in the presence of carbonic anhydrates, consequences are protons and carbonate ions. Hemoglobin binds protons and the affinity for oxygen is released. Binding for protons makes structural changes in protein, affinity for oxygen decreases. The binding of protons is associated with structural changes---facilitates release of oxygen. In addition of the affect of protons, there is allosteric modulator of protein in red blood cells. Bound in such way that only when protein bound 2,3 dpg---protein becomes stabilized so lower affinity for oxygen, fascilitate release for oxygen in cells. Increase concentration of dpg, increase p50, decrease pH----- decrease affinity. The first place to look is heme iron. There is some structural difference between the relationship between heme iron and its 4 parole nitrogens ( iron buried into the 4 paroles prostetic group). Nitrogen that is absolon nitrogen of the heme linked histidine the 8 th amino acid of 6 th helix---change of structure of orbitals of iron when oxygen is bound. Measure spin of the iron use magnetic resonance. alterations of spin is a reflection of how electrons are distributed among the orbitls in metaloorganic complex. The main
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concenquence of change is cause heme linked histidine to BEND. When oxygen is bound— rearrangement of the electrons in the iron and in ligands makes it impossible for heme link histidine to have bend to the iron---unfavoreable van der waals. The heme linked histidine accommodates for this overlaps by moving laterally a little to releave overlaps. Consequence of such shifting in terms of overall protein structure is subtle but profound (part of helix). If
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This note was uploaded on 01/30/2010 for the course BIO 351 taught by Professor Hoffmann,j during the Fall '08 term at SUNY Stony Brook.

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Lec 15 - Lec 15 Hemoglobin and myoglobin Hemoglobin is...

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