Hemoglobin

Hemoglobin is one of the first proteins to be studied by X-ray crystallography, for which Max Perutz was awarded the Nobel Prize in 1962 (Ahmed 2020).

The term "hemoglobin" refers to an iron-containing, oxygen-binding protein of erythrocytes that has peroxidase properties (Gressner 2019).

Hemoglobin occurs as:

- Hemoglobin A0

This is the most common hemoglobin in adults, accounting for 97.5 %. It consists of two alpha and two beta chains (Kietzmann 2023).

- Free haemoglobin (hemoglobin in plasma)

Free haemoglobin is the haemoglobin freely present in the plasma. It is produced in small quantities in the RES during the breakdown of erythrocytes. It is bound to haptoglobin and returned to the RES (Gressner 2019).

- Glycated haemoglobin (glycated hemoglobin)

Glycated haemoglobin is haemoglobin bound to various carbohydrates, most commonly a combination with glucose (Gressner 2019).

- Haemoglobin in urine (hemoglobin in urine)

Microscopically or macroscopically detectable haemoglobin in urine. This can be caused by prerenal causes, such as haemolysis, poisoning, severe infectious diseases, etc., renal causes, such as various kidney diseases, and postrenal causes, such as bleeding in the urinary tract (Gressner 2019).

- Haemoglobin A1

Haemoglobin A1 is a mixture of HbA glycated with various carbohydrates (Gressner 2019).

- Haemoglobin A1c

When blood glucose levels are elevated, part of the haemoglobin is covalently glycosylated to haemoglobin A1c due to the presence of glucose in the plasma (Silverthro2009).

The hemoglobin A1c value reflects the average blood glucose level of the last 3 months and therefore plays an important role in the long-term control of diabetes mellitus. A value of ≤ 5.7 % is considered normal, a value of > 6.5 % is considered diabetic (Fung 2022).

- Haemoglobin A2

Haemoglobin A2 also consists of two alpha and two delta chains and, at 2.5%, is rarely found in adults (Kietzmann 2023).

- Haemoglobin F (HbF)

This is found in 100 % of fetuses and 75 % of newborns. It consists of two alpha and two gamma chains and has a higher oxygen affinity than HbA0. HbF is exchanged for HbA0 during the first three months of life (Kietzmann 2023).

Over 1000 naturally occurring variants of haemoglobin have now been discovered, some of which have been assigned to disease patterns. However, the majority of these variants have not yet been assigned to any disease entity (Ahmed 2020).

Different haemoglobins are formed during embryonic, foetal and adult life (Kasper 2015).

Erythrocytes consist of 34 % haemoglobin. Haemoglobin is therefore the most important haem protein in the blood (Kietzmann 2023).

Haemoglobin is synthesized exclusively in the erythrocyte precursor cells; its degradation takes place in cells of the reticuloendothelial system (RES), particularly in the spleen (Gressner 2019). The heme groups are converted into bilirubin, which is secreted via the intestine as a component of bile and largely excreted in the feces (Silverthorn 2009).

The reference range of hemoglobin is gender-dependent at:

- Women: 123 - 153 g / l

- Men: 140 - 175 g / l (Gressner 2019)

A decrease in hemoglobin is called anemia, an increase is called polyglobulia (Gressner 2019).

Haemoglobin is present in the erythrocytes in such a high concentration that it can influence the shape, viscosity and deformability of the erythrocytes (Kasper 2015).

In the human body, most of the iron is bound to haemoglobin (Herold 2022). Iron serves as a means of transport for oxygen (Schmuck 2008).

Haemoglobin is crucial for the normal supply of oxygen (Kasper 2015). One gram of haemoglobin can bind 1.34 ml of oxygen. Around 40 - 50 % of the haemoglobin in venous blood is saturated with oxygen. The remaining globulin transports carbon dioxide (Marino 2008).

The determination of haemoglobin - together with haematocrit - plays an important role in the diagnosis of anaemia and polyglobulia (Gressner 2019).

Haemoglobin consists of various globin chains. Each of these chains encloses a single heme moiety, which in turn contains an iron atom. Each of these haem parts can bind a single oxygen molecule, and each haemoglobin molecule can transport up to 4 oxygen molecules (Kasper 2015).

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