l-myo-Inositol-1-Phosphate Synthase Expressed in Developing Organ: Isolation and Characterisation of the Enzyme from Human Fetal Liver

l-myo-inositol-1-phosphate synthase (MIPS; EC: 5.5.1.4) activity has been detected and partially purified for the first time from human fetal liver. Crude homogenate from the fetal liver was subjected to streptomycin sulphate precipitation and 0–60 % ammonium sulphate fractionation followed by successive chromatography through DEAE cellulose and BioGel A 0.5-m columns. After the final chromatography, the enzyme was purified 51-fold and 3.46 % of MIPS could be recovered. The human fetal liver MIPS specifically utilised d-glucose-6-phosphte and NAD+ as its substrate and coenzyme, respectively. It shows pH optima between 7.0 and 7.5 while the temperature maximum was at 40 °C. The enzyme activity was remarkably stimulated by NH 4 + , slightly stimulated by K+ and Ca2+ and highly inhibited by Zn2+, Cu2+ and Hg2+. The K m values of MIPS for d-glucose-6-phosphate and NAD+ were found to be as 1.15 and 0.12 mM respectively while the V max values were 280 nM and 252 nM for d-glucose-6-phosphate and NAD+ correspondingly. The apparent molecular weight of the native enzyme was determined to be 170 kDa.