Involvement of thermoplasmaquinone-7 in transplasma membrane electron transport of Entamoeba histolytica trophozoites: a key molecule for future rational chemotherapeutic drug designing.

The quinone composition of the transplasma membrane electron transport chain of parasitic protozoa Entamoeba histolytica was investigated. Purification of quinone from the plasma membrane of E. histolytica and its subsequent structural elucidation revealed the structure of the quinone as a methylmenaquinone-7 (thermoplasmaquinone-7), a napthoquinone. Membrane bound thermoplasmaquinone-7 can be destroyed by UV irradiation with a concomitant loss of plasma membrane electron transport activity. The abilities of different quinones to restore transplasma membrane electron transport activity in UV irradiated trophozoites were compared. The lost activity was recovered completely by the addition of thermoplasmaquinone-7, but ubiquinones are unable to restore the same. These findings clearly indicate that thermoplasmaquinone-7 acts as a lipid shuttle in the plasma membrane of the parasite to mediate electron transfer between cytosolic reductant and non permeable electron acceptors. This thermoplasmaquinone-7 differs from that of the mammalian host and can provide a novel target for future rational chemotherapeutic drug designing.