Hemozoin

Hemozoin is a disposal product formed from the digestion of blood by some blood-feeding parasites. Haematophagous organisms such as Malaria parasites (Plasmodium spp.), Rhodnius and Schistosoma digest hemoglobin and release high quantities of free heme, which is the non-protein component of hemoglobin. A heme or haem is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. This process is much-studied in Plasmodium since it is an attractive target for developing drugs to treat malaria.

Formation
The monomeric and potentially toxic α-hematin (ferriprotoporphyrin IX) is detoxified by biocrystallization into insoluble, chemically inert ß-hematin crystals (hemozoin). Several mechanisms have been proposed for this reaction and the area is controversial, with membrane lipids, histidine-rich proteins, or even a combination of the two, being proposed to catalyse the formation of hemozoin.

Structure
In ß-hematin a unique iron oxygen coordinate bond links the central iron of one heme to the oxygen of the carboxylate side chain of the adjacent heme. β-hematin can either be a cyclic dimer or a linear polymer, a polymeric form has never been found in hemozoin. Hemozoin crystals have a distinct triclinic structure and are weakly magnetic. They also exhibit optical dichroism, which means that they absorb light more strongly along their length than across their width, and this allows the automated detection of malaria. Hemozoin is produced in a form that under the action of an applied magnetic field gives rise to an induced optical dichroism characteristic of the hemozoin concentration and  precise measurement of this induced dichroism may be used to determine the level of malarial infection.