The presence of free Hb not only affects the oxygen carrying capacity of the blood, but also impacts other protein systems and organ function, but the mechanisms are not well understood. Even mild intravascular hemolysis may cause damage to the glycocalyx of endothelial cells and irregularity of the vascular smooth muscle tone. Although the main function of Hb in most mammals is to carry oxygen, similar proteins are found in other species with the function of scavenging various forms of oxidation byproducts. This is also evident in mammalian species where hemoglobin can bind CO₂ for transport back to the lungs as well as the nearly irreversible binding of carbon monoxide (CO) by hemoglobin, which makes CO poisoning in low CO environments possible. Similar to CO, hemoglobin also has a high affinity for nitric oxide (NO). This affinity for NO may be a mechanism for some of the sequelae that result from the release of hemoglobin into the plasma where it can bind the available NO, which is an important molecule for smooth muscle cell relaxation and associated vasodilation.