Formation of haemozoin/beta-haematin under physiological conditions is not spontaneous.
Malaria parasite detoxifies free haem, released as a result of haemoglobin digestion, by converting it into an stable, crystalline, black brown pigment known as 'malaria pigment' or 'haemozoin'. Earlier studies have demonstrated the involvement of a parasite-specific enzyme 'haem polymerase' in the formation of haemozoin. However, recently it has been proposed that the polymerization of haem may be a spontaneous process that could take place by incubation of haematin with carboxylic acids (pH 4.2-5.0) even without presence of any parasitic or biological component (FEBS Letters, 352, 54-57 (1994). Here we report that no spontaneous haem polymerization occurs at physiological conditions and the product described in the study mentioned above is not haemozoin/beta-haematin (haem polymer) as characterized by us on the basis of solubility characteristics and thin layer chromatography. The infra-red spectroscopic analysis of the product formed though exhibits the bands corresponding to formation of iron-carboxylate bond, similar to that in haemozoin/beta-haematin, but was identified as haem-acid adduct. Thus polymerization of haem may not occur spontaneously under the reaction conditions corresponding to food vacuoles of the malarial parasite, the physiological site of haemozoin formation.
Pandey
A V
AV
Division of Biochemistry, Central Drug Research Institute Lucknow, (UP), India.
Tekwani
B L
BL
D000818:Animals; D004912:Erythrocytes / Q000378:metabolism / Q000469:parasitology*; D006420:Hemeproteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D006427:Hemin / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism*; D008099:Liver / Q000469:parasitology; D008288:Malaria / Q000097:blood / Q000503:physiopathology; D010860:Pigments, Biological / Q000096:biosynthesis; D010967:Plasmodium yoelii / Q000302:isolation & purification / Q000502:physiology*; D013055:Spectrophotometry, Infrared; D014166:Transferases / Q000378:metabolism
D006420:Hemeproteins; D006454:Hemoglobins; D010860:Pigments, Biological; C020753:hemozoin; D006427:Hemin; D014166:Transferases; C072176:heme polymerase