Degradation of inositol 1,3,4,5-tetrakisphosphates by porcine brain cytosol yields inositol 1,3,4-trisphosphate and inositol 1,4,5-trisphosphate

Properties of a soluble inositol 1,3,4,5-tetrakisphosphate 3-phosphatase from porcine brain

“…The 3-dephosphorylation of Ins(1,3,4,5)P4 was also described by us in the soluble fraction of porcine brain [10], and in RBL-2H34 cells by Cunha-Melo et al [11]. Cullen-et al [12] recently showed that Ins(1,3,4,5)P4 causes release of Ca2+ by its rapid conversion to Ins(1,4,5)P3 in electroporated mouse lymphoma L1210 cells via a 3-phosphatase.…”

“…causing 50% inhibition 265 mM). The enzyme described by us is activated by KCI [10] and is therefore not identical with the Ins(1,3)P2 phosphatase from bovine brain.…”

“…It is independent of Mg2+ and is not inhibited by Li+. We cannot exclude the possibility that the enzyme from porcine brain, which is also independent of Mg2+ and Li' [10], is identical with this Ins(1,3)P2 3-phosphatase. An Ins(1,3)P2 phosphatase in bovine brain has recently been described [18].…”

“…All nucleotides and Ins (3,4,5,6) [5-32P]Ins(1,3,4,5)P4 was prepared as described previously [10] and was checked for isomeric purity using a Partisphere WAX column as described [8], which enables the separation of InsP4 isomers. Analysis of radiolabelled InsP4 showed that the prepared [5-32P] Estimation of molecular mass The molecular mass of the 3-phosphatase was determined by gel filtration at 4 'C on a Superose 6 column (1 cm x 30 cm) equilibrated with buffer consisting of 100 mM-NaCl, 1 mM-EDTA, 1 mM-DTT and 20 mM-Hepes/NaOH, pH 7.0.…”

“…

We have previously shown that Ins(1,3,4,5)P4 is degraded to Ins(1,4,5)P3 by a soluble Ins(1,3,4,5)P4 3-phosphatase from pig brain [Hoer, Kwiatkowski, Seib, Rosenthal, Schultz & Oberdisse (1988) by Mg2" up to 30 mm or Ca2l up to 1 mm. Commercially available Ins(3,4,5,6)P4 from turkey erythrocytes produced a marked inhibition of the 3-phosphatase (Ki 500 nM).

…”