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Localization of ferrochelatase in Plasmodium falciparum

Varadharajan, Sundaramurthy and Sagar, Chandrashekar BK and Rangarajan, Pundi N and Padmanaban, Govindarajan (2004) Localization of ferrochelatase in Plasmodium falciparum. In: Biochemical Journal, 384 (2). pp. 429-436.

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Our previous studies have demonstrated de novo haem biosynthesis in the malarial parasite (Plasmodium falciparum and P. berghei). It has also been shown that the first enzyme of the pathway is the parasite genome-coded ALA ($\delta$-aminolaevulinate) synthase localized in the parasite mitochondrion, whereas the second enzyme, ALAD (ALA dehydratase), is accounted for by two species: one species imported from the host red blood cell into the parasite cytosol and another parasite genome-coded species in the apicoplast. In the present study, specific antibodies have been raised to PfFC (parasite genome-coded ferrochelatase), the terminal enzyme of the haem-biosynthetic pathway, using recombinant truncated protein. With the use of these antibodies as well as those against the hFC (host red cell ferrochelatase) and other marker proteins, immunofluorescence studies were performed. The results reveal that P. falciparum in culture manifests a broad distribution of hFC and a localized distribution of PfFC in the parasite. However, PfFC is not localized to the parasite mitochondrion. Immunoelectron-microscopy studies reveal that PfFC is indeed localized to the apicoplast, whereas hFC is distributed in the parasite cytoplasm. These results on the localization of PfFC are unexpected and are at variance with theoretical predictions based on leader sequence analysis. Biochemical studies using the parasite cytosolic and organellar fractions reveal that the cytosol containing hFC accounts for 80% of FC enzymic activity, whereas the organellar fraction containing PfFC accounts for the remaining 20%. Interestingly, both the isolated cytosolic and organellar fractions are capable of independent haem synthesis in vitro from $[4-^1^4C]$ALA, with the cytosol being three times more efficient compared with the organellar fraction. With $[2-^1^4C]$glycine, most of the haem is synthesized in the organellar fraction. Thus haem is synthesized in two independent compartments: in the cytosol, using the imported host enzymes, and in the organellar fractions, using the parasite genome-coded enzymes.

Item Type: Journal Article
Additional Information: The copyright of this article belongs to The Biochemical Society.
Keywords: apicoplast,ferrochelatase,haem synthesis,localization,mitochondrion,Plasmodium falciparum.
Department/Centre: Division of Biological Sciences > Biochemistry
Depositing User: Anka Setty
Date Deposited: 26 Feb 2007
Last Modified: 19 Sep 2010 04:24
URI: http://eprints.iisc.ac.in/id/eprint/5881

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