Biosynthesis of Myo-Inositol in Chloroplasts of Salinity-Stressed Marine Macro Alga Ulva lactuca

Abstract

The present communication reports enhanced myo-inositol biosynthesis under natural conditions in Ulva lactuca Linn. based on the study conducted on its two prime enzymes [L-myo-inositol-1-phosphate synthase (MIPS) and myo-inositol-1-phosphate phosphatase (MIPP)] involved in myo-inositol biosynthesis. The two key enzymes obtained from chloroplastidial sources were partially purified to about 49- and 58-fold, respectively, over the homogenate following low speed centrifugation, high speed centrifugation, 0–80% ammonium sulphate precipitation and successive chromatography using ion exchange, gel filtration and molecular sieve packed columns. MIPS preparations specifically utilized D-glucose-6-phosphate and NAD as its exclusive substrate and coenzyme, while MIPP preparations used D/L-myo-inositol -1- phosphate as its principal substrate. Using non-linear regression kinetics method, the Km values of MIPS for G-6-P and NAD were calculated to be 2.6340 mM and 0.1271 mM, while the Km value of MIPP for D-MIP was recorded to be 0.02128 mM. Both enzymes were remarkably active within a temperature range of 20–40°C, and the optimum pH for both enzymes were found to be 7.5. Different cations and organic modifiers exhibited variable effects on the activity of both enzymes. The content of free myo-inositol was found to increase proportionately with the increase of surface salinity of the Chilika Lagoon, Odisha, India.