Structure
Hemoglobin is a protein in the human body that has important functions for the transport of oxygen in the blood. Proteins in the human body are always made up of multiple amino acids linked together. The amino acids are partly taken up by the body with food, partly the body can also convert other molecules into amino acids through enzymatic conversions or produce them completely by itself.
141 individual amino acids link together to form a subunit of hemoglobin, a globin. A hemoglobin molecule consists of four globins, with two identical subunits each forming a molecule. The globines are folded to form a kind of pocket into which a heme molecule, a so-called “iron complex”, is bound.
This iron complex, of which there are four in a hemoglobin molecule, binds one molecule each of oxygen, one O2. Due to the iron in its structure, the hemoglobin takes on a red color, which gives the whole blood its color. If the iron ion now binds an oxygen molecule, the color of the hemoglobin changes from dark red to a lighter red.
This color change is also noticeable when comparing venous and arterial blood. The arterial blood, which carries more oxygen bound, has a much lighter color. The four globin subunits have a special effect in binding the four oxygen molecules.
With each oxygen molecule that is bound, interactions between the four subunits occur and the binding of another oxygen molecule is facilitated. A hemoglobin loaded with four oxygen molecules is particularly stable. The release works in the same way.
Once one molecule of oxygen leaves the hemoglobin, the process is facilitated for the other three as well. In different life situations, humans have different forms of hemoglobin. As a child in the womb, he has first embryonic and later fetal hemoglobin.
The globin subunits differ in their chemical structure and cause the infantile hemoglobin to have a significantly higher affinity for oxygen than the hemoglobin of adult humans. This enables the oxygen to be transferred from the mother’s blood to the child’s blood in the placenta. The adult human can have two different types of hemoglobin, HbA1 or HbA2, although HbA1 is predominant in 98% of all people.
If blood sugar levels remain too high over a long period of time, a hemoglobin coupled with sugar, the HbA1c, may be present. In diagnostics, it is mainly used to analyze long-term blood sugar levels. Methemoglobin is a non-functional form.
It can no longer bind oxygen. It is present in small amounts in every person and is formed particularly strongly in smoke inhalation or genetic defects. The higher the proportion, the greater the oxygen deficiency for the human organism.
The function of hemoglobin in the human body is vital. The iron molecule in the center of the heme, which is carried by each globin subunit, binds an oxygen molecule. After the venous blood in the body is pumped from the right heart to the lungs, it accumulates there with the inhaled oxygen.
From then on it is called oxygen-rich. Over the boundaries of the pulmonary alveoli, the oxygen diffuses through the vessel walls, into the red blood cells, the erythrocytes, and binds chemically to the iron ion. The blood takes on the typical light red arterial color due to the binding and is then pumped through the body from the left heart via the large bloodstream.
At the tissue that is to supply the blood with oxygen, the blood flows particularly slowly through the capillaries so that the oxygen-deficient tissue can extract the O2 molecule from the oxygen-rich blood and the hemoglobin is converted back to its original form. The effect of “cooperativeness” causes the four globin units to mutually facilitate the loading and unloading of oxygen molecules. If one oxygen molecule is already bound, the binding of the other three molecules is greatly facilitated.
As a result, the oxygen content remains stable for the time being, even with slight limitations in oxygen enrichment. Even restrictions in old age, stays in heights and slight lung dysfunction do not initially have a strong influence on the oxygen saturation of the blood. Even if the partial pressure of oxygen in the air we breathe has already dropped to half of its original value, the oxygen saturation of the blood is still over 80%.It is also very important that hemoglobin has the property of binding oxygen to different degrees depending on pH, CO2 partial pressure, temperature and 2,3-BPG (2,3-bisphosphoglycerate).
This allows as much as possible to be bound in the lungs and as much as possible to be released in the rest of the body tissue when needed. The 2,3-BPG, which is increasingly produced during altitude training, for example, also enables the body to reduce the binding strength of oxygen so that it can be released more easily. In addition, hemoglobin also has the function of transporting CO2 to a certain extent and releasing it into the lungs.
In this process, the carbon dioxide is also bound to the hemoglobin, but not to the binding site of the O2. For many diseases, the hemoglobin value is significant. Especially the deficiency diseases, which are called anemias, are a common problem.
