|Ribbon / surface model of the 2x (hemoglobin-α / β / Hpβ) -hexamer from pork ( Sus scrofa ), according to PDB 4f4o , consisting of two Hbα / Hbβ / Hpβ-trimers (Hap = pink, middle), heme as domes .|
|Properties of human protein|
|Mass / length primary structure||774 = 2 * (142 + 245) amino acids|
|Secondary to quaternary structure||2 alpha + 2 beta|
|Precursor||(388 amino acids)|
|Gene names||; MGC111141; hp2-alpha|
Haptoglobin (Hp) is a blood plasma Represented transport and acute-phase protein belonging to the group of α₂ globulins belongs. It is made by the liver and released into the blood. Its task is to bind and transport hemoglobin in order to break it down in the reticuloendothelial system (RES) and to prevent the excretion of iron via the kidneys and their damage by hemoglobin. The binding takes place specifically and firmly to the globin part of the hemoglobin. The resulting complex is broken down within a few minutes. If the accumulation of hemoglobin exceeds the binding capacity of the haptoglobin, hemoglobinemia occurs . By binding to haptoglobin, free hemoglobin is not only kept away from the kidneys, it cannot cause oxidative cell damage and it is no longer available as a substrate for bacteria in the event of infections .
Siegfried-Ernst Miederer first discovered in 1966 at the Univ. Obtain a protein that could bind hemoglobin during perfusion tests on the isolated kidney. This protein is called haptoglobin.
Haptoglobin consists of 4 polypeptide chains , two light ( α ) and two heavy ( β ). The light chains, which can exist in two variants ( α₁ or α₂ ), have similarities in the sequence of their amino acids to those of the immunoglobulins , the heavy chains have a trypsin- like protease effect and are on the breakdown of globin after cleavage of the porphyrin ring of the heme involved in the liver.
A distinction is made between homozygous Hp 1-1 and Hp 2-2 and heterozygous Hp 1-2 types, which differ in the combination of the α₁, α₂ and β chains and (because of their different weights) therefore also in their electrophoretic pattern distinguish. The first-mentioned phenotype is increasingly found in Africans and Central and South Americans , the second in Asians , and the third in Central Europeans .
Haptoglobin is the most sensitive marker of hemolysis available. By lowering the free haptoglobin (i.e. with an increased removal of hemoglobin for degradation), hemolysis can therefore be recognized under certain circumstances, in which the other available markers (e.g. potassium, LDH, indirect bilirubin) are still normal. In this context, haptoglobin is a crucial marker for HELLP syndrome , a serious maternal emergency in obstetrics.
Its concentration is around 2 g / l, the maximum binding capacity at around 3 g / l. The reference range (normal range) in the serum is age and sex dependent and is approximately 0.5-2.5 g / l. In the case of hemolysis , the value is reduced.
In the case of hemolysis , the haptoglobin concentration (the free haptoglobin is measured ) is reduced, in the case of Hodgkin's disease , malignancies and necrosis, and inflammation, it is increased. Since it is formed in the liver , when interpreting the findings it must also be taken into account that in combination with existing liver diseases it can also be normal or decreased. Conversely, despite intravascular hemolysis, the haptoglobin value can be normal if there is inflammation at the same time, so that the C-reactive protein (CRP) must also be determined here so that an indication of the presence of inflammation is not overlooked.
- J. Pintera: The protective influence of haptoglobin on hemolytic kidney. In: Folia haemat. (Leipzig) 90, 1968, p. 82.
- SE Miederer: A contribution to the pathogenesis of the hemolytic kidney. In: Bruns' contribution clin. Chir. 217, 1969, pp. 661-665.
- UniProt P00738 .
- haptoglobin. In: Online Mendelian Inheritance in Man . (English).