Hemoglobin

Structure of human hemoglobin.
The α and β subunits are in red and blue.
The iron-containing heme groups in green

Hemoglobin (or haemoglobin) is a protein in red blood cells which contains iron. It is used to transport oxygen around the human body.^[1]

Hemoglobin is found in the red blood cells of almost all vertebrates. The exceptions are the fish family Channichthyidae,^[2] and the tissues of some invertebrates.^[3] It does occur in some invertebrates, but most invertebrates use other chemicals, such as hemocyanin.

Hemoglobin is involved in the transport of other gases. It carries some of the body's respiratory carbon dioxide (about 20-25% of the total).^[4]

Red blood cells get their colour from hemoglobin, which is red. There are millions of hemoglobin molecules in each red blood cell and millions of red blood cells in the human body. When hemoglobin has oxygen attached, it is called oxyhemoglobin.

Structure

The most common type of hemoglobin in mammals contains four such subunits. Each subunit of hemoglobin is a globular protein (globin) with a heme group inside it. Each heme group has one iron atom. This binds one oxygen molecule. So the complete hemoglobin molecule has four globin chains, four heme molecules, and four iron atoms.^[5] When hemoglobin is in the lungs, it picks up oxygen in its hemes, and carries it to the rest of the body.

Its structure took years to work out. Max Perutz and John Kendrew worked out the structure of myoglobin first. That muscle globin is smaller, with only one heme group.

Hemoglobin Media

Max Perutz won the Nobel Prize for chemistry for his work determining the molecular structure of hemoglobin and myoglobin
An alignment of human hemoglobin alpha, beta, and delta from UniProt. (after Engelhart 1825 - Adair 1925, Hünefeld 1840, Funke 1851,
Hemeb
A schematic visual model of oxygen-binding process, showing all four monomers and hemes, and protein chains only as diagrammatic coils, to facilitate visualization into the molecule. Oxygen is not shown in this model, but, for each of the iron atoms, it binds to the iron (red sphere) in the flat heme.
The sigmoidal shape of hemoglobin's oxygen-dissociation curve results from cooperative binding of oxygen to hemoglobin.
Gene expression of hemoglobin before and after birth. Also identifies the types of cells and organs in which the gene expression (data on Wood W.G., (1976). Br. Med. Bull. 32, 282.)
A hemoglobin concentration measurement being administered before a blood donation at the American Red Cross Boston Blood Donation Center.
The giant tube worm Riftia pachyptila showing red hemoglobin-containing plumes
Heart of Steel (Hemoglobin) (2005) by Julian Voss-Andreae. The images show the 5-foot (1.50 m) tall sculpture right after installation, after 10 days, and after several months of exposure to the elements.