hemoglobin

[ hee-muh-gloh-bin, hem-uh- ]

noun

, Biochemistry.

1. the oxygen-carrying pigment of red blood cells that gives them their red color and serves to convey oxygen to the tissues: occurs in reduced form deoxyhemoglobin in venous blood and in combination with oxygen oxyhemoglobin in arterial blood. : Hb

hemoglobin

/ hē′mə-glō′bĭn /

1. An iron-containing protein present in the blood of many animals that, in vertebrates, carries oxygen from the lungs to the tissues of the body and carries carbon dioxide from the tissues to the lungs. Hemoglobin is contained in the red blood cells of vertebrates and gives these cells their characteristic color. Hemoglobin is also found in many invertebrates, where it circulates freely in the blood. It consists of four peptide units, each attached to a nonprotein compound called heme that binds to oxygen.
2. See Note at red blood cell

hemoglobin

1. A complex organic molecule (see also organic molecules ) containing iron that carries oxygen in the blood .

Notes

Hemoglobin gives blood its characteristic red color.

Other Words From

• he·mo·glo·bic [hee-m, uh, -, gloh, -bik], he·mo·glo·bin·ous [hee-m, uh, -, gloh, -bi-n, uh, s], adjective

Word History and Origins

Origin of hemoglobin¹

First recorded in 1865–70; earlier hematoglobulin; hemo-, globulin

A Closer Look

Ninety percent of the protein in red blood cells is made up of hemoglobin, the main oxygen transport molecule in mammals. A protein with four iron-containing subunits called hemes, hemoglobin is a complex molecule with a complex function. It must bind to oxygen in the lungs, then release that oxygen in the tissues, then bind to carbon dioxide in the tissues and release it in the lungs. Hemoglobin accomplishes oxygen transport by changing its structure, and even its substructures, around the oxygen-binding heme groups, making them more or less accessible to the environment. When oxygen binds to at least one of the heme groups (as happens in the oxygen-rich lungs), all of the heme groups become exposed to the environment and bind oxygen easily. The bond between oxygen and heme is a loose one, however, so that the oxygen can break free in the tissues, where the concentration of oxygen is relatively low, and thereby become available for use in the cells. When the last of the four heme subunits loses its oxygen, the structure of hemoglobin changes again, so that the size of the opening from the environment to the heme groups decreases, making it difficult for an oxygen molecule to rebind to the hemoglobin. In this way, hemoglobin stops itself from competing with the tissues for needed oxygen. When the red blood cell carrying hemoglobin returns to the lungs, where oxygen concentration is high, the cycle of oxygen binding, transport, and release starts again. Normally, iron binds with oxygen to form rust (iron oxide), but the structure of hemoglobin prevents this from happening, since it would inactivate the heme subunits. Carbon dioxide does not bind the heme in hemoglobin, but rather the amino groups at the ends of the hemoglobin's protein subunits. Hemoglobin transport is only one of a number of bodily mechanisms by which carbon dioxide travels from the tissues to the lungs for release to the air.

Example Sentences

The researchers tracked participants' blood pressure, a marker for blood clot and stroke risk; measured hemoglobin levels to check whether the pumps were breaking red blood cells; and monitored patients for other complications.

From Science Daily

Part of this is due to changes in the regulation of the EPAS1 gene, which lowers hemoglobin concentrations by regulating the pathway that responds to changing oxygen levels.

From Science Daily

This results from either lower than normal levels of red blood cells or a decrease in the quantity or quality of hemoglobin, the protein that allows these cells to transport oxygen.

From Salon

This is the first time cytoglobin -- or any of the globin proteins like hemoglobin -- has been found to be involved in fetal development and that a paucity could be linked to birth defects.

From Science Daily

Sickle cell disease affects hemoglobin, the protein in red blood cells that carries oxygen.

From Washington Times

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