Hemoglobin and Myoglobin (Hb/Mb)

Hemoglobin and myoglobin are structurally related but functionally distinct globular hemeproteins that play central roles in vertebrate oxygen transport and storage. Hemoglobin is a heterotetrameric protein found primarily in red blood cells, responsible for the cooperative, reversible transport of oxygen from lungs to tissues and removal of carbon dioxide. Myoglobin is a monomeric muscle protein with higher oxygen affinity than hemoglobin; it acts as a reservoir and facilitator of oxygen diffusion within skeletal and cardiac muscle. Both proteins bind molecular oxygen via a central iron atom in a porphyrin (heme) group, but their quaternary structure imparts distinct oxygen-binding kinetics: sigmoidal for hemoglobin and hyperbolic for myoglobin. Clinically, hemoglobin abnormalities cause several hematologic diseases, while myoglobin serves as a sensitive biomarker for muscle injury and myocardial infarction. Drugs and toxicants can disrupt the function of both proteins through competitive oxygen binding or oxidation of the heme iron. Both are not "classic" drug targets like G protein-coupled receptors or enzymes, but are crucial for pathophysiology, diagnostics, and for understanding oxygen homeostasis in health and disease.

Other names

HaemoglobinHbHemoglobin A (adult)Hemoglobin S (sickle)Hemoglobin F (fetal)Hemoglobin subunit alphaHemoglobin subunit betaMbmuscle hemoprotein

Reversible oxygen binding via cooperative (allosteric) binding in the heme site for Hemoglobin; drugs/toxins act by displacing oxygen (e.g., CO binding, cyanide inhibition). For Myoglobin, reversible oxygen binding is non-cooperative with hyperbolic kinetics; toxins/drugs behave analogously (e.g., carbon monoxide forms carboxymyoglobin).