IDENTIFICATION AND PURIFICATION OF FE CONTAINING SUPEROXIDE DISMUTASE FROM LEISHMANIA DONOVANI
Bikramjit Raychaudhury*, R. Jyoti, Kakuli Chakraborty, Anindita Chakraborty, Moushree Palroy and Rajen Haldar
Leishmaniasis is a parasitic disease which infects as many as 400,000 people per year. Because the infective agent- a protozoan-inhabits phagolysosomes in host macrophages, the parasites are partially protected from chemotherapeutic agents. Thus, treated patients often relapse or experience toxic reactions to the drugs. In order to develop new leishmanicidal agents, studies have been conducted to understand the interactions of the parasite with the macrophage. Ordinarily, microorganisms which are taken up by macrophages are destroyed by oxygen-dependent and oxygen-independent antimicrobial systems. The oxygen-dependent antimicrobial activity of macrophages is dependent on the generation of superoxide (O2-) by the one-electron reduction of molecular oxygen. This O2- can then undergo a series of reactions to produce hydrogen peroxide (H2O2), hydroxyl radicals (.OH), and perhaps, singlet oxygen (1O2), which may be responsible for destroying the ingested microorganism. Some microorganisms, such as Toxoplasma gondii, block the generation of superoxide by macrophages in order to survive phagocytosis. It is found that this was not the case for Leishmania. The uptake of Leishmania tropica promastigotes by mouse peritoneal macrophages was accompanied by the generation of high levels of superoxide and other activated forms of oxygen. The possibility that parasites might survive phagocytosis by efficient enzymatic decomposition of H2O2 and O2- has also been investigated. The parasites were found to lack or contain low levels of enzymes capable of decomposing H2O2 (glutathione peroxidase and catalase) but to contain relatively high levels of superoxide dismutase, which degrades O2-. Evidence was obtained that the leishmanial superoxide dismutase was substantially different from the superoxide dismutase found in its host and therefore made a potential target for the design of parasite-specific enzyme inhibitors. The leishmanial superoxide dismutase activity was found to be insensitive to inhibition by cyanide, but sensitive to inhibition by azide and peroxide, properties which suggest an Fe containing superoxide dismutase. In contrast, the mammalian host has only Cu/Zn-containing and Mn-containing superoxide dismutases. In order to further characterize the leishmanial superoxide dismutase, we have isolated superoxide dismutase from Leishmania donovani.
Keywords: Leishmania donovani, Superoxide dismutase, Antioxidant.
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