Hemoglobin
Carbon monoxide has a higher diffusion coefficient compared to oxygen, and the main enzyme in the human body that produces carbon monoxide is heme oxygenase, which is located in nearly all cells and platelets. Most endogenously produced CO is stored bound to hemoglobin as carboxyhemoglobin. The simplistic understanding for the mechanism of carbon monoxide toxicity is based on excess carboxyhemoglobin decreasing the oxygen-delivery capacity of the blood to tissues throughout the body. In humans, the affinity between hemoglobin and carbon monoxide is approximately 240 times stronger than the affinity between hemoglobin and oxygen. However, certain mutations such as the Hb-Kirklareli mutation has a relative 80,000 times greater affinity for carbon monoxide than oxygen resulting in systemic carboxyhemoglobin reaching a sustained level of 16% COHb.Hemoglobin is a tetramer with four prosthetic heme groups to serve as oxygen binding sites. The average red blood cell contains 250 million hemoglobin molecules, therefore 1 billion heme sites capable of binding gas. The binding of carbon monoxide at any one of these sites increases the oxygen affinity of the remaining three sites, which causes the hemoglobin molecule to retain oxygen that would otherwise be delivered to the tissue; therefore carbon monoxide binding at any site may be as dangerous as carbon monoxide binding to all sites. Delivery of oxygen is largely driven by the Bohr effect and Haldane effect.
Brachymetacarpia is a medical condition in which the metacarpals of the hands are shortened, the foot equivalent to this condition is brachymetatarsia. This condition is one of the causes of brachydactyly.