1L-MYO-INOSITOL-1-PHOSPHATE SYNTHASE

1L-myo-Inositol-1-phosphate synthase catalyzes the conversion of D-glu cose 6-phosphate to 1L-myo-inositol-1-phosphate, the first committed s tep in the production of all inositol-containing compounds, including phospholipids, either directly or by salvage. The enzyme exists in a c ytoplasmic form in a wide range of plants, animals, and fungi. It has also been detected in several bacteria and a chloroplast form is obser ved in alga and higher plants. The enzyme has been purified from a wid e range of organisms and its active form is a multimer of identical su bunits ranging in molecular weight from 58 000 to 67 000. The activity of the synthase is stimulated by NH4Cl and inhibited by glucitol 6-ph osphate and 2-deoxyglucose 6-phosphate. Structural genes (INO1) encodi ng the 1L-myo-inositol-1-phosphate synthase subunit have been isolated from several eukaryotic microorganisms and higher plants. In baker's yeast, Saccharomyces cerevisiae, the transcriptional regulation of the INO1 gene has been studied in detail and its expression is sensitive to the availability of phospholipid precursors as well as growth phase . The regulation of the structural gene encoding 1L-myo-inositol-1-pho sphate synthase has also been analyzed at the transcriptional level in the aquatic angiosperm, Spirodela polyrrhiza and the halophyte, Mesem bryanthemum crystallinum. (C) 1997 Elsevier Science B.V.