Haemozoin is a disposal product formed from the digestion of blood by some blood-feeding parasites. These hematophagous organisms such as malaria parasites (Plasmodium spp.), Rhodnius and Schistosoma digest haemoglobin and release high quantities of free heme, which is the non-protein component of haemoglobin. Heme is a prosthetic group consisting of an iron atom contained in the center of a heterocyclic porphyrin ring. Free heme is toxic to cells, so the parasites convert it into an insoluble crystalline form called hemozoin. In malaria parasites, hemozoin is often called malaria pigment.
Since the formation of hemozoin is essential to the survival of these parasites, it is an attractive target for developing drugs and is much-studied in Plasmodium as a way to find drugs to treat malaria (malaria's Achilles' heel). Several currently used antimalarial drugs, such as chloroquine and mefloquine, are thought to kill malaria parasites by inhibiting haemozoin biocrystallization.
Black-brown pigment was observed by Johann Heinrich Meckel in 1847, in the blood and spleen of a person suffering from insanity. However, it was not until 1849 that the presence of this pigment was connected to infection with malaria. Initially, it was thought that this pigment was produced by the body in response to infection, but Charles Louis Alphonse Laveran realized in 1880 that "malaria pigment" is, instead, produced by the parasites, as they multiplied within the red blood cell. The link between pigment and malaria parasites was used by Ronald Ross to identify the stages in the Plasmodium life cycle that occur within the mosquito, since, although these forms of the parasite are different in appearance to the blood stages, they still contain traces of pigment.
Later, in 1891, T. Carbone and W.H. Brown (1911) published papers linking the hemoglobin degradation with pigment production, describing the malaria pigment as a form of hematin and disproving the widely held idea that it is related to melanin.
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Biocrystallization is the formation of crystals from organic macromolecules by living organisms. This may be a stress response, a normal part of metabolism such as processes that dispose of waste compounds, or a pathology. Template mediated crystallization is qualitatively different from in vitro crystallization. Inhibitors of biocrystallization are of interest in drug design efforts against lithiasis and against pathogens that feed on blood, since many of these organisms use this process to safely dispose of heme.
Plasmodium falciparum is a unicellular protozoan parasite of humans, and the deadliest species of Plasmodium that causes malaria in humans. The parasite is transmitted through the bite of a female Anopheles mosquito and causes the disease's most dangerous form, falciparum malaria. It is responsible for around 50% of all malaria cases. P. falciparum is therefore regarded as the deadliest parasite in humans. It is also associated with the development of blood cancer (Burkitt's lymphoma) and is classified as a Group 2A (probable) carcinogen.
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