CO binds tightly to the Hb Fe(II) forming HbCO.

When CO binds to the 4 heme sites, Hb shifts to the R state causing a shift in the O2 binding curve.: from sigmoidal to a hyperbola.

The affinity of Hb for CO is 220 times greater than for oxygen.

CO poisoning is treated with 100% O2 therapy.

At 1-10%, no symptoms are exhibited.

At 10-30%, possibly slight headache and throbbing in temples.

At 30-50%, severe headache, weakness and dizziness, nausea, vomiting, and dim vision

50-60%, coma with convulsions.

60-80%, depressed heart action and respiration, as well as respiratory failure and death

- CO competes for O2-binding sites on hemoglobin.  The affinity of hemoglobin for CO is 200 times its affinity for O2.
- CO occupies O2-binding sites on hemoglobin, thus decreasing the O2-binding capacity of hemoglobin and decreasing the O2 content of blood.
- In addition, binding of CO to hemoglobin increases the affinity of remaining sites for O2, causing a shift of the oxygen-binding curve to the left.