L-myo-InositoL-1- phosphate synthase from bryophytes: purification and characterization of the enzyme from Lunularia cruciata (L.) Dum

L-myo-inositol-1-phosphate synthase (MIPS; EC: 5.5.1.4) catalyzes the conversion of D-glucose-6-phosphate to 1L-myo-inositol-1-phosphate, the rate limiting step in the biosynthesis of all inositol containing compounds. Myo-inositol and its derivatives are implicated in membrane biogenesis, cell signaling, salinity stress tolerance and a number of other metabolic reactions in different organisms. This enzyme has been reported from a number of bacteria, fungi, plants and animals. In the present study some bryophytes available in the Eastern Himalaya have been screened for free myo-inositol content. It is seen that Bryum corinatum, a bryopsid shows the highest content of free myo-inositol among the species screened. Subsequently , the enzyme MIPS has been partially purified to the tune of about 70 fold with approximately 18% recovery form the reproductive part bearing gametophytes of Lunularia cruciata. The L. cruciata synthase specifically utilized D-glucose-6-phosphate and NAD+ as its substrate and co-factor respectively. The optimum pH shown was 7.0 while the temperature maximum was at 30oC. The enzyme activity was slightly stimulated by Mg2+ and Ca2+; remarkably stimulated by NH4+; slightly inhibited by Mn2+; highly inhibited by Cu2+, Zn2+ and Hg2+. The Km values for D-glucose-6-phosphate and NAD+ was found to be 0.80 and 0. 034 mM respectively while the Vmax values were 2.8 and 1.21 mM for D-glucose-6-phosphate and NAD+ respectively.