What does carbon monoxide (CO) bind to in the blood, disrupting its function?

Carbon monoxide (CO) has a high affinity for hemoglobin, the protein in red blood cells responsible for transporting oxygen throughout the body. When CO is inhaled, it can bind to hemoglobin more effectively than oxygen does, forming carboxyhemoglobin. This binding significantly reduces the amount of hemoglobin available to carry oxygen, leading to a decrease in oxygen delivery to tissues and organs. The consequence is that even if there is sufficient oxygen in the air, the body cannot utilize it effectively due to the presence of carbon monoxide. This mechanism is why CO is considered highly toxic and poses serious health risks, including suffocation at elevated concentrations. The other substances listed, like carbon dioxide, nitrogen oxide, and sulfur dioxide, do not have the same direct and detrimental effect on hemoglobin's ability to transport oxygen.