A novel method for the purification of inositol phosphates from biological samples reveals that no phytate is present in human plasma or urine

Inositol phosphates are a large and diverse family of signalling molecules. Whilegenetic studies have discovered important functions for them, the biochemistrybehind these roles is often not fully characterized. A key obstacle in inositolphosphate research in mammalian cells has been the lack of straightforwardtechniques for their purification and analysis. Here we describe the ability oftitanium dioxide (TiO₂) beads to bind inositol phosphates. Thisdiscovery allowed the development of a new purification protocol that, coupledwith gel analysis, permitted easy identification and quantification ofInsP₆ (phytate), its pyrophosphate derivatives InsP₇and InsP₈, and the nucleotides ATP and GTP from cell or tissueextracts. Using this approach, InsP₆, InsP₇ andInsP₈ were visualized in Dictyostelium extractsand a variety of mammalian cell lines and tissues, and the effects of metabolicperturbation on these were explored. TiO₂ bead purification alsoenabled us to quantify InsP₆ in human plasma and urine, which led totwo distinct but related observations. Firstly, there is an activeInsP₆ phosphatase in human plasma, and secondly, InsP₆is undetectable in either fluid. These observations seriously question reportsthat InsP₆ is present in human biofluids and the advisability ofusing InsP₆ as a dietary supplement.