Preparation of 1L-myo-Inositol 1-Phosphate as a Substrate of Phosphatidylinositol Phosphate Synthase

Novel drugs possessing a mechanism of action specific to pathogenic mycobacteria, including Mycobacterium tuberculosis, are needed. In 2010, we discovered that the biosynthetic pathway of phosphatidylinositol, which is a membrane phospholipid, differs between humans and mycobacteria. The key enzyme responsible for this difference is phosphatidylinositol phosphate (PIP) synthase, which is present only in a few bacteria belonging to the phylum Actinobacteria. Discovering compounds that inhibit the activity of this enzyme will lead to the development of new drugs specific to pathogenic mycobacteria. Measuring PIP synthase activity requires the isotope-labeled substrate 1l-myo-inositol 1-phosphate (1l-Ino-1P). Because this substrate is not commercially available, we synthesized it from [14C] glucose 6-phosphate ([14C] Glc-6P), using a crude enzyme solution isolated from the methanoarchaeon 1l-Ino-1P synthase. The activity of 1l-Ino-1P synthase in the crude enzyme mixture was low, and quantitative analysis of the synthesized 1l-Ino-1P was inaccurate due to impurities present in the crude enzyme mixture. In the present study, we describe a method for synthesizing 1l-Ino-1P using a solution containing recombinant 1l-Ino-1P synthase derived from the hyperthermophilic archaeon Aeropyrum pernix. In addition, we elucidate the conditions leading to the almost complete conversion of Glc-6P into 1l-Ino-1P using this enzyme. Quantitation of the synthesized 1l -Ino-1P was performed by colorimetry and gas liquid chromatography. Further, we confirmed that isotope-labeled 1l-Ino-1P, which is difficult to quantitate by gas liquid chromatography, can be accurately quantified by colorimetry. We also confirmed that 1d-inositol 1-phosphate cannot be a substrate for PIP synthase.