Confusion with binding curve for CO

[deleted647690]

I know that CO causes an increase in the affinity of Hb for oxygen. I would expect that to shift the normal sigmmoidal binding curve of Hb to the left, so that it resembles a hyperbola shifted to the left, since the affinity is increased and it will not release O2 to the tissues.
Why is this not correct? My textbook shows it as shifting to the right, which I don't understand, because wouldn't that mean that the affinity for O2 is decreased? Meaning that more O2 would be released to the tissues?

Here's what I'd expect:

Apparently, this isn't correct. This is correct,

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[reinesupreme]

Are you sure your book is correct? Look at this thread:

http://forums.studentdoctor.net/threads/co-and-hemoglobin-curve.732716/

It's supposed to shift left.

 

[popopopop]

Top colored graph has hgb saturation for y axis, so CO shifts left* because of higher affinity like you said.

Bottom graph has volume of dissolved oxygen in blood for y axis, so it's lower when COHb is present. That's my guess.

 

[exposedbrickcampaign]

Ok so I have a 7 level biochem course at well as a 3 level bioinorganic course this term so I can help.
Top graph shows the hyperbolic curve of CO-Hb binding -VS- the sigmoidal curve of O2-Hb binding. It is comparing the binding of CO to Hb VS O2 to Hb. Period, nothing more!!
Bottom graph shows the graph for O2 binding to Hb. Again, it is sigmoidal as expected. The line for 50% COHb indicates that when the air is 50% CO and 50% O2, the Hb affinity for O2 drops. When the blood is anemic (either half the original blood volume is missing OR all of the original blood volume is present but half of it lacks Fe 2+, again, the Hb affinity for O2 drops.
You must understand that when it comes to Hb, CO and O2 COMPETITIVELY bind Hb. So both graphs are correct. The top shows Hb binding for TWO DIFFERENT gases SEPARATELY however for simplicity and direct comparison they are illustrated on the same graph.
Bottom graph shows that when O2 and CO are mixed, Hb binds less O2. Why? Bc Hb binds CO approx 250 times stronger than it binds O2.

 

[exposedbrickcampaign]

So no, CO does NOT increase Hb's binding affinity for O2. Again, CO and O2 compete for Hb. Therefore CO decreases Hb's affinity to bind O2.

 

[exposedbrickcampaign]

Furthermore, O2 binding to Hb is subject to a phenomenon called cooperativity (1 O2 binding causes Hb to bind the next O2 more strongly. the first two bound O2 causes the 3rd O2 to bind even more strongly etc), hence the sigmoidal curve. CO does not display this phenomenon, therefore its curve is hyperbolic. Take away, the hyperbolic shape can NOT become sigmoidal for any reason. And the sigmoidal can NOT become hyperbolic for any reason.

 

[Gibbward]

@exposedbrickcampaign now use your bioinorganic chemistry and MO diagram skills to explain why CO has a higher affinity to Hb compared to O2!! (Just kidding... I just love seeing people take bioinorganic! Definitely my favorite area of basic science research.)