title: Inositol Trisphosphate Metabolism in Subcellular Fractions of Barley (Hordeum vulgare L.) Mesophyll Cells.
abstract: Phosphatases in cytosolic fractions, vacuoles, and vacuolar membranes from barley (Hordeum vulgare L.) leaves were found to dephosphorylate inositol 1,4,5-trisphosphate (IP3). 1,4-inositol bisphosphate (1,4-IP2) is the main product of IP3 dephosphorylation by the cytosolic fraction. The activity was strictly Mg2+ dependent. In contrast, IP3 dephosphorylation activity of both the soluble vacuolar and the tonoplast fractions was inhibited up to 50% by Mg2+. When vacuolar membranes were incubated with IP3, 1,4-IP2 was produced only under neutral and slightly alkaline conditions. Under acidic conditions, however, dephosphorylation yielded putative 4,5-inositol bisphosphate. Li+ (20 mM) and Ca2+ (100 [mu]M) strongly inhibited activity in the soluble vacuolar fraction but had only a slight effect on the activities of the cytosolic and tonoplast fractions.
authors.affiliation: Institute of Plant Sciences, Swiss Federal Institute of Technology, Zurich Sonneggstrasse 5, ETH-Z, CH-8092 Zurich, Switzerland (E.M., E.V.).
authors.forename: E.
authors.initials: E
authors.lastname: Martinoia
authors.forename: R.
authors.initials: R
authors.lastname: Locher
authors.forename: E.
authors.initials: E
authors.lastname: Vogt