neo-Inositol polyphosphates in the amoeba Entamoeba histolytica

We have reexamined the structure of inositol phosphates resent in trophozoi tes of the parasitic amoeba Entamoeba histolytica and show here that, rathe r than being myo-inositol derivatives (Martin, J.-B., Bakker-Grunwald, T., and Klein, G. (1993) fur. J, Biochem 214, 711-718), these compounds belong to a new class of inositol phosphates in which the cyclitol isomer is neo-i nositol. The structures of neo-inositol hexakisphosphate, 2-diphospho-neo-i nositol pentakisphosphate, and 2,5-bisdiphospho-neo-inositol tetrakisphosph ate, which are present in E. histolytica at concentrations of 0.08-0.36 mM, were solved by two-dimensional P-31-H-1 NMR spectroscopy. No evidence for the co-existence of their myo-inositol counterparts has been found. These n eo-inositol compounds were not substrates of 6-diphospho-inositol pentakisp hosphate Fi-kinase, an enzyme purified from Dictyostelium discoideum that p hosphorylates 6-diphospho-myo-inositol pentakisphosphate and more slowly al so myo-inositol hexakisphosphate, specifically on position 5. Because preli minary data indicate that large amounts of the same neo-inositol phosphate and diphosphate esters are also present in another primitive amoeba, Phreat amoeba balamuthi, the occurrence of high concentrations of neo-inositol pol yphosphates may be much more general than previously thought.