The enzymes involved in the synthesis of phytic acid in Lemna gibba (studies on the biosynthesis of cyclitols, XL.(1)).

The biosynthesis of phytic acid is known to be catalyzed by enzymes causing a stepwise phosphorylation of myo-inositol or 1L-myo-inositol 1-phosphate with adenosine triphosphate as phosphate donor. The kinase responsible for these phosphorylations in Lemna gibba were purified by affinity chromatography on a Sepharose gel carrying myo-inositol 2-phosphate at the binding site. Three fractions with enzymatic activity could be identified; in the first one, we find myo-inositol kinase (EC 2.7.1.64) phosphorylating myo-inositol to 1L-myo-inositol 1-phosphate; the second one brings about the phosphorylation of myo-inositol trisphosphate to phytic acid; the third one phosphorylates myo-inositol 1-phosphate to a myo-inositol trisphosphate. An enzyme oxidizing 1L-myo-inositol 1-phosphate to an uronic acid derivative is found in the first two fractions. In the presence of ATP, Mg2+, Mn2+, and the second and the third enzyme fractions in an appropraite mixture, 1L-myo-inositol 1-phosphate can be phosphorylated to phytic acid. The structure of the trisphosphate acting as an intermediate is not yet known.