dragon72

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Dec 7, 2005
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question: why the conversion from normal hemoglobin to methemoglobin causes the dissociation curve to shift left instead of right. If it shift left then affinity for oxygen would increase and that is wrong. I don 't understand why.

Thanks in advance,
Andy
 

DrChandy

10+ Year Member
7+ Year Member
Apr 28, 2004
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Medical Student
dragon72 said:
question: why the conversion from normal hemoglobin to methemoglobin causes the dissociation curve to shift left instead of right. If it shift left then affinity for oxygen would increase and that is wrong. I don 't understand why.

Thanks in advance,
Andy
It is true that methemoglobin (and carbon monoxide) produce a shift to the left of the oxygen dissociation curve, rather than to the right as one would expect, but for the MCAT, know that this is more of an exception to the general idea of the O2 dissociation curve.

For the MCAT, know the general idea of how the oxygen dissociation curve works (which it seems like you already do), and the situations which cause shifts to the left and right respectively.

The shift of the curve to the left in the case of methemoglobin and carbon monoxide is probably due to (one or more) chemical factors being released by the body as a compensatory mechanism in order to maintain steady O2 levels (by increasing Hb affinity for oxygen) in situations of lower functional Hb concentration.
 
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