Diphospho-myo-inositol phosphates from Dictyostelium identified as D-6-diphospho-myo-inositol pentakisphosphate and D-5,6-bisdiphospho-myo-inositol tetrakisphosphate

Two diphospho-myo-inositol phosphates from Dictyostelium were recently investigated by two-dimensional ¹H/³¹P NMR analysis and assigned to be either D-4-diphospho-myo-inositol pentakisphosphate (D-4-PP-InsP₅) and D-4,5-bisdiphospho-myo-inositol tetrakisphosphate (D-4,5-bis-PP-InsP₄) or their corresponding enantiomers D-6-PP-InsP₅ and D-5,6-bis-PP-InsP₄. In the present study the naturally occurring enantiomers were identified by using defined synthetic PP-InsP₅ isomers as substrates for a partially purified PP-InsP₅ 5-kinase from Dictyostelium. This enzyme specifically phosphorylates the naturally occurring PP-InsP₅ and the synthetic D-6-PP-InsP₅, leading to D-5,6-bis-PP-InsP₄. In contrast, neither D-4-PP-InsP₅ nor D-1-PP-InsP₅ or D-3-PP-InsP₅ are converted by the enzyme.