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 Ca(2+) and highly inhibited by Zn(2+), Cu(2+) and Hg(2+). 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.