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  • Title: Characterization of D-myo-inositol 1,4,5-trisphosphate phosphatase in rat liver plasma membranes.
    Author: Seyfred MA, Farrell LE, Wells WW.
    Journal: J Biol Chem; 1984 Nov 10; 259(21):13204-8. PubMed ID: 6092366.
    Abstract:
    D-myo-Inositol 1,4,5-trisphosphate has been previously demonstrated to act as a second messenger for the hormonal mobilization of intracellular calcium in rat liver. In this study, the breakdown of D-myo-inositol 1,4,5-trisphosphate by a phosphatase activity was characterized. Using partially purified subcellular fractions, it was found that D-myo-inositol 1,4,5-trisphosphate phosphatase (I-P3ase) specific activity was highest in the plasma membrane fraction, while D-myo-inositol 1,4-bisphosphate phosphatase specific activity was highest in the cytosolic and microsomal fractions. The plasma membrane I-P3ase was Mg2+-dependent with optimal activity observed at 0.5-1.5 mM free Mg2+. The enzyme had a neutral pH optimum, suggesting that it was neither an acid nor alkaline phosphatase. Neither LiCl nor NaF inhibited the I-P3ase activity. However, both L-cysteine and dithiothreitol stimulated the activity 2-fold. Spermine (2.0 mM) inhibited the I-P3ase activity by 50%, while putrescine and spermidine had little or no effect.
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