Subcellular localization and kinetic properties of phosphatidylinositol 4,5-bisphosphate phospholipase C and inositol phosphate enzymes from human peripheral blood mononuclear cells |
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| Authors: | R Graber G A Losa |
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| Affiliation: | Laboratorio di Patologia Cellulare, Istituto Cantonale di Patologia, Locarno, Switzerland. |
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| Abstract: | Peripheral blood mononuclear cells from normal donors exhibited phosphatidylinositol 4,5-bisphosphate phospholipase C (PIP2-PLC), inositol 1,4,5-trisphosphate (IP3) and inositol 1-phosphate (IP)-monophosphatase activities which were mostly recovered in the cytosol fraction. In both cytosol and particulate fractions PIP2-PLC displayed the highest activity at pH 6.2, whereas IP3 and IP-monophosphatases showed the same optimal pH at 7.0. While the PIP2-PLC displayed close apparent Km values in cytosol and particulate fractions, both inositol-monophosphatases were found to show substrate affinities for IP and IP3 characteristic of these two fractions, with an higher affinity in the soluble fraction. |
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