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>And the saga continues... (g) > >>Scott, >> >>Let me check, but I do not think that the statement: >> >>>4) CO binding is so thermodynamically favorable that binding is, >>>practically speaking, permanent, essentially removing the bound >>>hemo site from the pool of available transport. >> >>is quite accurate. At sealevel, with only 0.21 ATA of oxygen partial >>pressure, this statement is essentially true, but in the presence of >>high enough partial pressures of oxygen, monoxide will unbind from >>hemoglobin. "Further more, it bind with about 230 times as much tenacity >>as oxygen, which is illustrated by the carbon monoxide-hemoglobin >>dissociation curve in Figure 41-12 (this is take from Guyton's "Textbook >>of Medical Physiology", page 511 and 512). This curve is almost identical >>with the oxygen-hemoglobin dissociation curve, except that the pressures >>of the carbon monoxide shown on the abscissa are at a level 1/230 of those >>on the oxygen dissociation curve. Therefore, a carbon monoxide pressure >>of only 0.4 torr in the alveoli, 1/230 that of the alveolar oxygen, allows >>the carbon moxide to COMPETE equally wit# the hemoglobin and causes half to >>the hemoglobin in the blood to become bound with monoxide instead of >oxgyen." > >Aren't we really saying the same thing? That ratio adds up to an >overwhelming thermodynamic favorability for the CO binding over O2 >in my book. And, barring administration of unusual and artificial >driving forces to that reaction, the hemoglobin would certainly >remain bound for the servicable lifetime of the molecule. >Unusual and artificial driving forces such as high-pressure >O2, aka one treatment for CO posioning. > carboxyhaemoglobin half-life in air is about 5.5 hours regards, David Doolette ddoolett@me*.ad*.ed*.au*
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