Biochemistry of Entamoeba: A review

Abstract

Entamoeba histolytica, the protozoan parasite causing amoebiasis, is carried by approximately 10% of the world's population although only a minority of carriers of the organism present active clinical symptoms.Although Entamoeba are classified as eukaryotes, the biochemistry of these organisms has a number of unusual facets which are reminiscent of prokaryotes. It has indeed been suggested that these cells represent early evolutionary forms that have been successful in surviving unchanged in the protected environment in which they reproduce (the intestine).Glycolysis in Entarnoeba lacks several of the typical eukaryotic glycolytic enzymes. The pentose phosphate shunt enzymes are missing completely. Another unusual feature of the glycolytic path is the utilization of PP, instead of ATP in a number of enzyme reactions e.g. phosphofructokinase. Entamoeba is the only eukaryote in which one of these PP, utilizing enzymes, phosphoenolpyruvate carboxytransferase, has been found.The respiratory pathway is also an unusual one. Entamoeba are classified as anaerobes but the cells do have an affinity for oxygen. The oxygen is reduced to water at the end of a respiratory chain which is not well understood but which operates withough cytochromes or mitochondria.The nucleic acid, protein and lipid metabolic pathways have not been well studied and interest has mainly focused on the proteolytic processes of the amoeba which have been implicated in the pathogenic, histolytic behavior of the parasite. Despite these efforts the mechanism of attack of the parasite and the stimuli that cause it to invade the host are not yet clear. This understandably is the goal of much of the present studies concerning E. histolytica but the organism also deserves study in its own right as an example of an organism that has an unusual biochemistry and may represent an early stage in the evolution of eukaryotic cells.