Heme Proteins

Author: Gianpiero Pescarmona
Date: 06/09/2010



Hemopexin , binds heme with the highest affinity of any known protein. Its function of scavenging the heme released or lost by the turnover of heme proteins.
Heme scavenging protects the organism from

  • heme requiring bacteria (Yersinia Pestis eg.)
  • oxidative damage


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When relevant for the function

  • Primary structure
  • Secondary structure
  • Tertiary structure
  • Quaternary structure

Protein Aminoacids Percentage
The Protein Aminoacids Percentage gives useful information on the local environment and the metabolic status of the cell (starvation, lack of essential AA, hypoxia)

Protein Aminoacids Percentage (Width 700 px)


mRNA synthesis
protein synthesis
post-translational modifications


cellular localization

Its messenger is found only in liver as its receptor.

hepatocytes, macrophages, and syncytiotrophoblasts.

The primary receptor for uptake of Hx-heme complexes is hitherto not identified.

The asialoform of Hx has been reported to recognize the asialoglycoprotein receptor, but this hepatocyte-specific receptor is suggested to represent a secondary receptor for catabolism of outdated Hx, which has lost the terminal sialic acids of the N-linked carbohydrates

biological function

Identification of the receptor scavenging hemopexin-heme complexes 2005

Heme released from heme-binding proteins on internal hemorrhage, hemolysis, myolysis, or other cell damage is highly toxic due to oxidative and proinflammatory effects. Complex formation with hemopexin, the high-affinity heme-binding protein in plasma and cerebrospinal fluid, dampens these effects and is suggested to facilitate cellular heme metabolism. Using a ligand-affinity approach, we purified the human hemopexin-heme receptor and identified it as the low-density lipoprotein receptor-related protein (LRP)/CD91, a receptor expressed in several cell types including macrophages, hepatocytes, neurons, and syncytiotrophoblasts. Binding experiments, including Biacore analysis, showed that hemopexin-heme complex formation elicits the high receptor affinity. Uptake studies of radio-labeled hemopexin-heme complex in LRP/CD91-expressing COS cells and confocal microscopy of the cellular processing of fluorescent hemopexin-heme complex established the ability of LRP/CD91 to mediate hemopexin-heme internalization resulting in cellular heme uptake and lysosomal hemopexin degradation. Uptake of hemopexin-heme complex induced LRP/CD91-dependent heme-oxygenase 1 mRNA transcription in cultured monocytes. In conclusion, hemopexin-heme complexes are removed by a receptor-mediated pathway showing striking similarities to the CD163-mediated haptoglobin-hemoglobin clearance in macrophages. Furthermore, the data indicate a hitherto unknown role of LRP/CD91 in inflammation.
In the cell, toxic effects of heme are prevented by the activity of the heme oxygenases (HOs), which cause breakdown of the porphyrin ring into biliverdin, carbon monoxide, and iron. Biliverdin is subsequently converted to bilirubin by the biliverdin reductase, whereas iron is bound to ferritin.

  • Enzymes
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  • Cell signaling and Ligand transport
  • Structural proteins



Hemopexin and nephrotic syndrome 2008

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