NAD+ mediated differential thermotolerance between chloroplastic and cytosolic L-myo-inositol-1-phosphate synthase from Diplopterygium glaucum (Thunb.) Nakai

Relative thermotolerance of the enzyme, L-myo-inositol-1-phosphate synthase (MIPS; EC: 5.5.1.4), from the chloroplastic and cytosolic sources of Diplopterygium glaucum was studied. The purification involved streptomycin sulphate precipitation, ammonium sulphate fractionation, ion-exchange chromatography, and molecular sieve chromatography. After the final chromatography, 16.62% of chloroplastic and 13.47% of cytosolic MIPS could be recovered. Between 15 degrees C and 55 degrees C, the two forms of MIPS exhibited differential thermal stability, which is related to the presence of the MIPS co-factor, NAD(+). Added NAD(+) increased the lower thermotolerance of the chloroplastic MIPS and the removal of 'built-in' NAD(+) decreased the higher thermal stability of the cytosolic MIPS.