A salt-activated inositol 1,3,4,5-tetrakisphosphate 3-phosphatase at the inner surface of the human erythrocyte membrane

T. Estrada-Garcia, A. Craxton, C. J. Kirk, R. H. Michell*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)

Abstract

The localization of the human erythrocyte membrane Ins(1,3,4,5)P4 3-phosphatase was investigated by saponin permeabilization of resealed 'isoionic' erythrocyte ghosts. This enzyme is active at the inner face of the plasma membrane, at the same site as a specific 5-phosphatase that degrades both Ins(1,4,5)P3 and Ins(1,3,4,5)P4. In the presence of EDTA, Ins(1,4,5)P3 was the only product of Ins(1,3,4,5)P4 metabolism. However, when Mg2+ was present both the 5-phosphatase and the 3-phosphatase attacked Ins(1,3,4,5)P4, directly forming Ins(1,3,4)P3 and Ins(1,4,5)P3; some Ins(1,4)P2 was also formed as a product of 5-phosphatase attack on the liberated Ins(1,4,5)P3 The Ins(1,3,4,5)P4 3-phosphatase was potently activated by KCl, thus making the route of metabolism of Ins(1,3,4,5)P4 by erythrocyte ghosts strikingly sensitive to variations in ionic strength: at 'cytosolic' K+ and Mg2+ levels, 3-phosphatase activity slightly predominated over 5-phosphatase. Ins(1,3,4,5)P4 3-phosphatase was potently inhibited by Ins(1,3,4,5,6)P5 and InsP6 at levels lower than those often observed within cells. This leaves open the question as to whether the cellular function of inositol polyphosphate 3-phosphatase is to participate in a physiological cycle that interconverts Ins(1,3,4,5)P4 and Ins(1,4,5)P3 or to metabolize other inositol polyphosphates in the cytosol compartment of cells.

Original languageEnglish
Pages (from-to)63-68
Number of pages6
JournalProceedings of the Royal Society B: Biological Sciences
Volume244
Issue number1309
DOIs
Publication statusPublished - 1 Jan 1991

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)
  • Immunology and Microbiology(all)
  • Environmental Science(all)
  • Agricultural and Biological Sciences(all)

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