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GSTs are divided into two groups: the membrane-bound microsomal and the cytosolic GSTs.
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Microsomal GSTs exist in homo- and hetero-trimerized forms with a single active site and function in the endogenous metabolism of leucotrienes and prostaglandins [8].
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In humans, cytosolic GSTs exist in the form of various dimerized isoenzyme classes: (A), ¦Ì (M), , (P), (T), (Z) and classes[8,13].
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Their existence in different forms has provided broad substrate specificities promoting detoxification of many toxic substances.
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Recently, the X-ray crystal structure of GST of the malaria-causing parasite, Plasmodium falciparum, was elucidated [14].
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The isoenzymes of GST are related in their aminoacid constituents and a little in their conformation except at specific regions, two of which are needed for activity.
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This distinguishing uniqueness is attributed to the catalytic hydrophobic site (H-site) and a glutathione-binding site (G-site), which offer diversity in specificities of the different isoenzymes for different substrates.
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In addition to their xenobiotic detoxification roles, human and parasitic GSTs have been implicated as lead actors in cellular drug resistances, which is a major factor in the failure of chemotherapy [15].
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Electrophilic alkylating anticancer and antiparasitic drugs have been reported to be either substrates or ligands for the different GST isoenzymes [16], and this forms the basis of cellular drug resistances.
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