title: A pathway for the interconversion of hexose and pentose in the parasitic amoeba Entamoeba histolytica.
abstract: Isotope studies indicate that hexose-to-pentose interconversion by axenic Entamoeba histolytica conserves the C-1 and C-6 hexose carbon atoms. Transketolase was readily identified in amoebal extracts, and transaldolase could not be demonstrated. However, sedoheptulose 7-phosphate is a substrate for the PPi-dependent amoebal phosphofructokinase, and sedoheptulose 1,7-bisphosphate is cleaved by amoebal aldolase to dihydroxyacetone phosphate and erythrose phosphate. Since these three enzymes catalyse physiologically reversible reactions, a non-oxidative pathway for hexose-pentose interconversion exists in amoebae in the absence of transaldolase. By using known amoebal enzyme, the conversion of ribose into fructose was confirmed in vitro. Some kinetic parameters of amoebal phosphofructokinase, transketolase and aldolase were determined.
mesh_terms: D000818:Animals; D004748:Entamoeba histolytica / Q000201:enzymology / Q000378:metabolism*; D005634:Fructose-Bisphosphate Aldolase / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D006601:Hexoses / Q000378:metabolism*; D007700:Kinetics; D008954:Models, Biological; D010429:Pentoses / Q000378:metabolism*; D010732:Phosphofructokinase-1 / Q000378:metabolism; D012313:RNA / Q000378:metabolism; D014174:Transketolase / Q000378:metabolism
chemical_list: D006601:Hexoses; D010429:Pentoses; D012313:RNA; D014174:Transketolase; D010732:Phosphofructokinase-1; D005634:Fructose-Bisphosphate Aldolase; D005947:Glucose