A steric mechanism for inhibition of CO binding to heme proteins

The crystal structures of myoglobin in the deoxy- and carbon monoxide-ligat ed states at a resolution of 1.15 angstroms show that carbon monoxide bindi ng at ambient temperatures requires concerted motions of the heme, the iron , and helices E and F for relief of steric inhibition. These steps constitu te the main mechanism by which heme proteins lower the affinity of the heme group for the toxic ligand carbon monoxide.