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The composition of haemozoin from Plasmodium falciparum
J O Ashong1, I P Blench, D C Warhurst
1Department of Medical Parasitology, London School of Hygiene and Tropical Medicine, UK.
Abstract:
Haemozoin (malaria pigment) was isolated from 2 strains of Plasmodium falciparum cultivated in vitro. The purest preparations contained 41 to 45% ferriprotoporphyrin IX and a glycine-rich polypeptide ('apohaemozoin') of approximately 14 kDa molecular weight which is synthesized by the parasite. In the two strains studied, NF54 and K1, it was calculated that about 15 and 18 iron porphyrin molecules, respectively, were associated with each molecule of apohaemozoin, which contained more hydrophobic amino acid residues in strain K1. One molecule of iron porphyrin was associated with every 9-10 amino acid residues in the haemozoin of both strains. Our observations support the idea that the intraerythrocytic malaria parasite, incapable of cleaving the haem ring, detoxifies the iron porphyrin residuum from haemoglobin digestion in a crystalline complex with a specially synthesized protein.
Insights
Malaria parasites detoxify toxic heme by forming a crystalline complex called haemozoin. This pigment consists of iron porphyrin and a parasite-synthesized protein, apohaemozoin.
Area of Science:
- Biochemistry
- Parasitology
- Molecular Biology
Background:
- Haemozoin, also known as malaria pigment, is a byproduct of hemoglobin digestion by the malaria parasite Plasmodium falciparum.
- The parasite is known to be incapable of cleaving the heme ring, suggesting a detoxification mechanism is in place.
Purpose of the Study:
- To characterize the composition and structure of haemozoin.
- To investigate the role of apohaemozoin in haemozoin formation.
- To understand the detoxification mechanism of iron porphyrin by Plasmodium falciparum.
Main Methods:
- Isolation of haemozoin from Plasmodium falciparum strains (NF54 and K1) cultured in vitro.
- Biochemical analysis to determine the composition of ferriprotoporphyrin IX and apohaemozoin.
- Molecular weight determination of apohaemozoin.
- Analysis of amino acid composition and hydrophobic residues.
Main Results:
- Pure haemozoin preparations contained 41-45% ferriprotoporphyrin IX and a ~14 kDa glycine-rich polypeptide, apohaemozoin.
- Apohaemozoin is synthesized by the parasite.
- Approximately 15-18 iron porphyrin molecules were associated with each apohaemozoin molecule in strains NF54 and K1, respectively.
- Strain K1's apohaemozoin had more hydrophobic amino acid residues compared to strain NF54.
- One iron porphyrin molecule was associated with every 9-10 amino acid residues in the haemozoin of both strains.
Conclusions:
- Haemozoin is a crystalline complex of ferriprotoporphyrin IX and parasite-synthesized apohaemozoin.
- Apohaemozoin plays a crucial role in detoxifying iron porphyrin, a toxic byproduct of hemoglobin digestion.
- The structural variations in apohaemozoin between strains may influence the efficiency of this detoxification process.