Chapter 5 - Oxygen Transport

Abstract

Globins are highly conserved proteins containing a heme (protoporphyrin) prosthetic group, which binds oxygen. Monomeric myoglobin maintains a store of oxygen in muscle for mitochondrial metabolism; tetrameric hemoglobin binds oxygen for transport in blood. Hemoglobin is an allosteric protein consisting of two α and two β subunits, which change in structure and interaction in response to oxygen and allosteric effectors. Oxygen exerts a positive, homotropic effect on oxygen binding; with a Hill coefficient of 2.7, hemoglobin is nearly saturated with oxygen in the lungs. Negative, heterotropic allosteric effectors, such as protons (Bohr effect) and CO2, promote the release of oxygen in peripheral tissue. 2,3-Bisphosphoglycerate also decreases the oxygen affinity of hemoglobin; this is an important adaptation to high altitude and pulmonary disease. Mutations in globin genes lead to a spectrum of structural and functional variants, some of which are pathogenic, such as HbS, which causes sickle cell disease.