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Hemoglobin

Synonym: haemoglobin
German: Hämoglobin

1 Definition

Hemoglobin is the iron-containing red blood pigment in red blood cells of vertebrates and its derivatives. It enables the transport of oxygen in the body.

2 Biochemistry

Hemoglobin is made up of cyclic tetrapyrrole which contains iron, an oxygen binding heme group as a prosthetic group, and a protein part (globin).

One hemoglobin molecule is a heterotetramer formed by two alpha- and two other subunits that make the classification of different hemoglobins possible. The majority of adult hemoglobin contains beta chains, whereas fetal hemoglobin contains gamma chains. Delta chains have been described as well.

Each of these subunits possesses a prosthetic group which is responsible for actually binding the oxygen. As a result one hemoglobin tetramer can bind four oxygen molecules in total.

3 Physiology

There are two variants of hemoglobin, depending on their oxygen-binding status:

Measuring hemoglobin plays an important role in the diagnosis of anemia and is done by determining the hemoglobin concentration (Hb) of a whole blood sample.

see also: hemoglobin synthesis, hemoglobin degradation

4 Clinical chemistry

Determining the hemoglobin concentration (Hb) is an integral part of general diagnostics. It can be used to gauge the blood's oxygen transport capacity and to diagnose anemia and polycythemia.

  g/dl mmol/l
Men 13,5–17,5 8,7–11,2
Women 12–16 7,5–9,9

Reference values for children depend on their age.

5 Conversion

Note: Press the "Umrechnen" button to convert between the units.

6 Variants

6.1 HbA1c

A high glucose concentration in the blood leads to increased non-enzymatic glycation of hemoglobin. HbA1c is the stable ketoamine which is formed by the glycation of β-hemoglobin in the second position of the amino acid valine. This reaction only takes place to a relevant extent in the case of a long-term increased glucose concentration, which is why it is used for the observation of blood sugar levels in diabetes patients.

6.2 Dyshemoglobins

Dyshemoglobins are hemoglobin derivatives that cannot be oxygenated because the oxygen binding sites at the central iron atom are blocked. An example is the oxidation of the iron ion into trivalent iron which results in methemoglobin (MetHb). Methemoglobin can be converted back to the original hemoglobin by the NADH dependent methemoglobin reductase. In healthy humans less than two per cent of hemoglobin is present as methemoglobin.

Other dyhemoglobins are carboxyhemoglobin (COHb) and sulfhemoglobin (SulfHb).

7 Mutations

Modified hemoglobin variants can form due to mutation of the globin chain amino acid sequence. An example is hemoglobin S (HbSS) which occurs in patients with sickle-cell anemia

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