Understanding inositol pyrophosphate metabolism and function: kinetic characterization of the DIPPs

Abstract We illuminate the metabolism and the cell-signaling activities of inositol pyrophosphates, by showing that regulation of yeast cyclin-kinase by 1-InsP 7 is not conserved for mammalian CDK5, and by kinetically characterizing Ddp1p/DIPP-mediated dephosphorylation of 1-InsP 7 , 5-InsP 7 and InsP 8 . Each phosphatase exhibited similar K m values for every substrate (range: 35–148 nM). The rank order of k cat values (1-InsP 7  > 5-InsP 7  = InsP 8 ) was identical for each enzyme, although DIPP1 was 10- to 60-fold more active than DIPP2α/β and DIPP3α/β. We demonstrate InsP 8 dephosphorylation preferentially progresses through 1-InsP 7 . Conversely, we conclude that the more metabolically and functionally significant steady-state route of InsP 8 synthesis proceeds via 5-InsP 7 .