Earlier studies in this laboratory had shown that the malarial parasite can 
synthesize heme de novo and inhibition of the pathway leads to death of the 
parasite. It has been proposed that the pathway for the biosynthesis of heme in 
Plasmodium falciparum is unique involving three different cellular compartments, 
namely mitochondrion, apicoplast and cytosol. Experimental evidences are now 
available for the functionality and localization of all the enzymes of this 
pathway, except protoporphyrinogen IX oxidase (PfPPO), the penultimate enzyme. 
In the present study, PfPPO has been cloned, expressed and shown to be localized 
to the mitochondrion by immunofluorescence microscopy. Interestingly, the enzyme 
has been found to be active only under anaerobic conditions and is dependent on 
electron transport chain (ETC) acceptors for its activity. The native enzyme 
present in the parasite is inhibited by the ETC inhibitors, atovaquone and 
antimycin. Atovaquone, a well known inhibitor of parasite dihydroorotate 
dehydrogenase, dependent on the ETC, inhibits synthesis of heme as well in P. 
falciparum culture. A model is proposed to explain the ETC dependence of both 
the pyrimidine and heme-biosynthetic pathways in P. falciparum.