FIGURE 1.
The pathway involved in the synthesis of inositol phosphates in S. cerevisiae. InsP3 serves as a substrate for the inositol kinase Ipk2, which phosphorylates both the D-6 and D-3 position hydroxyl groups to produce InsP5. InsP5 is phosphorylated by Ipk1 at 2-hydroxyl to generate InsP6. The synthesis of diphosphoinositol phosphates is mediated by two kinases; Kcs1 phosphorylates InsP5 into 5-PP-InsP4 and InsP6 into 5-PP-InsP5 (InsP7), and Vip1 phosphorylates InsP6 into InsP7 isomer 1-PP-InsP5. (PP)2-IP4 (InsP8) is generated by either Kcs1-mediated phosphorylation of 1-PP-InsP5 or Vip1-mediated phosphorylation of 5-PP-InsP5.