Biosynthesis of Di- myo -Inositol-1,1′-Phosphate, a Novel Osmolyte in Hyperthermophilic Archaea

Abstract

ABSTRACT Biosynthesis of di- myo -inositol-1,1′-phosphate (DIP) is proposed to occur with myo -inositol and myo -inositol 1-phosphate (I-1-P) used as precursors. Activation of the I-1-P with CTP and condensation of the resultant CDP-inositol (CDP-I) with myo -inositol then generates DIP. The sole known biosynthetic pathway of inositol in all organisms is the conversion of d -glucose-6-phosphate to myo -inositol. This conversion requires two key enzymes: l -I-1-P synthase and I-1-P phosphatase. Enzymatic assays using 31 P nuclear magnetic resonance spectroscopy as well as a colorimetric assay for inorganic phosphate have confirmed the occurrence of l -I-1-P synthase and a moderately specific I-1-P phosphatase. The enzymatic reaction that couples CDP-I with myo -inositol to generate DIP has also been detected in Methanococcus igneus . 13 C labeling studies with [2,3- 13 C]pyruvate and [3- 13 C]pyruvate were used to examine this pathway in M. igneus . Label distribution in DIP was consistent with inositol units formed from glucose-6-phosphate, but the label in the glucose moiety was scrambled via transketolase and transaldolase activities of the pentose phosphate pathway.