Further studies on myo-inositol-1-phosphatase from the pollen of Lilium longiflorum Thunb

myo-Inositol-1-phosphatase has been purified to homogeneity from Lilium longiflorum pollen using an alternative procedure which includes pH change and phenyl Sepharose column chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis shows that the enzyme is a dimer (subunit molecular weight, 29,000 daltons). The enzyme is stable at low pH values and is inactivated only below pH 3.0. In addition to 1L-and 1D-myo-inositol-1-phosphate, it shows high specificity for 1L-chiro-inositol-3-phosphate. As observed earlier with other primary phosphate esters, D-glucitol-6-phosphate and D-mannitol-6-phosphate are hydrolyzed very slowly. No activity is observed with inorganic pyrophosphate or myo-inositol pentaphosphate as substrate. The enzyme is inhibited by fluoride, sulfate, molybdate, and thiol-directed reagents. Partial protection against N-ethylmaleimide inhibition by substrate and Mg2+ together suggests sulfhydryl involvement at the active site.