Formation of haemozoin/β‐haematin under physiological conditions is not spontaneous

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Abstract
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/β‐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/β‐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.