Hemoglobin and its derivatives

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Hemoglobin is a red blood pigment that transports oxygen from the lungs to the tissues and transports CO2 and protons from peripheral tissues to the respiratory system.

náhled|Rozdíl mezi venózní a arteriální krví

The hemoglobin concentration in a healthy adult male is approximately 150 g / l, in an adult female about 140 g / l.  One gram of hemoglobin can bind up to 1.34 ml of oxygen.

Structure of hemoglobin

náhled|100px|Hemoglobin náhled|100px|Hem It is a tetrameric protein made up of four subunits. The two and two subunits are always identical.  There are four types of polypeptide chains, physiologically occurring hemoglobin, α, β, γ, and δ, which differ in the number and sequence of amino acids.  The tetramer consists of two α chains and two other types of chains that indicate the character of the whole hemoglobin molecule.  In adults, hemoglobin A predominates, with two β chains (146 amino acids) involved in addition to two α chains (141 amino acids).

Each subunit includes a polypeptide chain to which one heme is covalently attached.  The basis of the heme molecule is protoporphyrin, formed by 4 pyrrole nuclei connected by methenyl bridges with centrally bound iron.  Heme iron is a total of six bonds - it is connected to the nitrogen atoms of the pyrrole nuclei by four coordination bonds.  By another coordination valence, iron binds to the imidazole group of the amino acid histidine in the globin chain.  The sixth valence Fe is for the oxygen molecule (O₂).

Hemoglobin in the blood

Determination of hemoglobin in the blood is one of the most basic laboratory tests.  Blood hemoglobin is the main criterion for assessing whether it is anemia.  The term anemia is used when hemoglobin or erythrocytes fall below the lower limit of physiological levels. Anemia is a very common clinical finding.  This is a condition that leads to a reduction in oxygen binding capacity and a consequent tissue respiratory disorder.

Causes of Anemia

Anemia occurs when erythropoiesis is unable to meet the requirements for new red blood cells.  It develops as a result of blood loss or increased loss of red blood cells or insufficient red blood cell production.  The following is a list of some specific causes of anemia:

1. Anemia from increased blood loss:
   • Acute blood loss.
   • Chronic blood loss.
2. Anemia due to increased erythrocyte breakdown (hemolytic conditions).
   • Autoimmune hemolytic anemia (presence of antibodies against own erythrocytes).
   • Erythrocyte membrane disorder (deviation in erythrocyte membrane composition).
   • Hereditary erythrocyte enzyme defects (pyruvate kinase, glucose-6-phosphate dehydrogenase).
   • Unstable hemoglobin - hemoglobinopathies (e.g. hemoglobin S in sickle cell disease).
3. Anemia from decreased erythrocyte production:
   • Lack of substances needed for erythropoiesis (iron deficiency, vitamin B12 deficiency, folic acid deficiency, erythropoietin deficiency - chronic renal diseases, lack of other substances such as vitamins B1, B6).
   • Anemia due to chemical, physical and radiation damage.
   • Anemia in chronic inflammatory, infectious and cancerous diseases.

Elevated hemoglobin levels may be a sign of dehydration or chronic decreased pulmonary ventilation.  Rarely, it can be caused by some myeloproliferative conditions, such as polycythemia vera.

Principle of hemoglobin determination in blood

Oxidation of hemoglobin to methemoglobin:

HbFeII	+	[FeIII(CN)6]3−	→	HbFeIII	+	[FeII(CN)6]4−
Hemoglobin				Methemoglobin

Conversion of methemoglobin to cyanomethemoglobin:

HbFeIII	+	CN−	→	HbFeIIICN
Methemoglobin				Cyanomethemoglobin

The photometric determination is based on the oxidation of ferrous iron in hemoglobin with potassium ferrocyanide to ferric iron.  The resulting methemoglobin is converted to a very stable cyanomethemoglobin in a further reaction with potassium cyanide with a single broad absorption maximum in the visible region at 540 nm.

Assessment: The reference range for hemoglobin in the blood (B hemoglobin) for an adult male is 130-180 g / l and for a female 120-160 g / l.

Task: Determination of hemoglobin in the blood (pdf)

Hemoglobine in urine

__Hemoglobin v moči

Úkol: Průkaz krve a krevního barviva v moči (pdf)

Hemoglobin ve stolici – okultní krvácení

Průkaz okultního (skrytého) krvácení slouží k záchytu časných fází kolorektálního karcinomu, kdy je možná radikální a efektivní léčba. Vyšetření spočívá v zachycení stop krve ve stolici, používají se různé metodické postupy:

• Metody využívají pseudoperoxidázové aktivity hemoglobinu. Pacient musí držet 3 dny před vyšetřením dietu, vyloučit ze stravy nedovařené maso, salámy, banány, rajčata, nesmí užívat léky obsahující kyselinu askorbovou nebo acetylsalicylovou. Poté si pacient sám odebírá vzorky ze tří po sobě jdoucích stolic a aplikuje je na testovací karty. Vyhodnocení se provádí v laboratoři, princip je podobný jako u diagnostických proužků hemoPHAN
• Další metody jsou založeny na imunochemickém průkazu hemoglobinu pomocí protilátky proti lidskému hemoglobinu. Imunochemické metody jsou citlivější a specifičtější, není zapotřebí držet před vyšetřením dietu. Pozitivní výsledky musí být ověřeny dalšími diagnostickými metodami.

Úkol: Test na okultní krvácení v zažívacím traktu (pdf)

Deriváty hemoglobinu

__Deriváty hemoglobinu

Úkol: Spektrofotometrické vyšetření hemoglobinu a jeho derivátů (pdf)

Úkol: Orientační stanovení karbonylhemoglobinu (pdf)

Glykovaný hemoglobin HBA₁

__Glykovaný hemoglobin

Úkol: Stanovení glykovaného hemoglobinu (pdf)

Železo

__Železo

Úkol: Stanovení Fe v séru kolorimetrickou metodou (pdf)

Odkazy

Související články

• Karbonylhemoglobin
• Karbaminohemoglobin
• Methemoglobin
• Vyšetrenie hemoglobínu a jeho metabolizmu
• Hem

Reference

Kategorie:Biochemie Kategorie:Fyziologie