Metabolism of inositol 1,3,4,5-tetrakisphosphate by human erythrocyte membranes. A new mechanism for the formation of inositol 1,4,5-trisphosphate

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). Significant inhibitory effects on enzyme activity were also found with GTP and the pyrimidine nucleotides UTP and CTP. The kinetic data presented here suggest that the Ins(1,3,4,5)P4 3-phosphatase may be regulated by the intracellular concentrations of inositol tris-and tetrakis-phosphates.

Section: Introductionsupporting

confidence: 53%

Section: Resultsmentioning

confidence: 92%

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

Höer

Oberdisse

1990

“…These were distinguished by use of the Ins(1,4,5)P3 5-phosphatase ofhuman erythrocytes . Pre-vious studies assumed that this is the only inositol polyphosphate phosphatase in human erythrocyte membranes, but these membranes also contain a highly active Ins(1,3,4,5)P4 3-phosphatase (Doughney et al, 1988;EstradaGarcia et al, 1991;A. Craxton & T. Estrada-Garcia, unpublished work).…”

Section: Inositol Bisphosphatesmentioning

confidence: 99%

The inositol phosphates in WRK1 rat mammary tumour cells

Wong

Barker

Morris

et al. 1992

1. A detailed structural survey has been made of the inositol phosphates of unstimulated and vasopressin-stimulated WRK-1 rat mammary tumour cells. Inositol phosphate peaks were separated by h.p.l.c., and structural assignments were made for more than 20 compounds by combinations of: (a) co-chromatography with labelled standards; (b) site-specific enzymic dephosphorylation; (c) complete and partial periodate oxidation, followed by h.p.l.c. of polyols and their stereospecific oxidation by dehydrogenases; and (d) ammoniacal hydrolysis. 2. The ‘inositol monophosphates’ fraction from unstimulated cells included an uncharacterized peak, probably containing some glycerophosphoinositol, and Ins(1:2-cyclic)P. Stimulation provoked accumulation of both Ins1P and Ins3P, of Ins2P, and of Ins5P and/or the enantiomers Ins4P and Ins6P. The proportions of Ins1P and Ins3P were determined by partial periodate oxidation and enantiomeric identification of the resulting glucitols. 3. Three inositol bisphosphate peaks were detected in unstimulated cells: Ins(1,4)P2 [this was distinguished chemically from its enantiomer Ins(3,6)P2], Ins(3,4)P2 and/or Ins(1,6)P2, and Ins(4,5)P2 and/or Ins(5,6)P2. On stimulation, Ins(1,4)P2 and Ins(3,4)P2 [and/or Ins(1,6)P2] levels increased, and Ins(1:2-cyclic,4)P2 and Ins(1,3)P2 were also formed. 4. Three inositol trisphosphate peaks were obtained from unstimulated cells: all increased during stimulation. These were Ins(1,3,4)P3 [with some Ins(1:2-cyclic,4,5)P3], Ins(1,4,5)P3 and Ins(3,4,5)P3 [and/or Ins(1,5,6)P3]. During stimulation, another compound, probably Ins(1,4,6)P3, appeared in the ‘Ins(1,4,5)P3 peak’. The ‘Ins(3,4,5)P3 peak’ contained a second trisphosphate, probably Ins(2,4,5)P3. 5. Three inositol tetrakisphosphates, namely Ins(1,3,4,6)P4, Ins(1,3,4,5)P4, were present in unstimulated cells, and all accumulated during stimulation. 6. Ins(1,3,4,5,6)P5, which is the most abundant inositol polyphosphate in these cells, a less abundant inositol pentakisphosphate and inositol hexakisphosphate were all unresponsive to stimulation.

“…detection, the intracellular concentrations of both the pentakisphosphate and the hexakisphosphate were found to be 5-15 /LM in various tissues of mammals [28]. In fMet-Leu-Phestimulated HL-60 cells, Pittet et al [29] [10][11][12]30] or permeabilized cells [31,32]. In the latter system, the endogenous inositol pentakis-and hexakis-phosphate will be diluted by the incubation buffer.…”

Section: Resultsmentioning

confidence: 99%

Inositol 1,3,4,5,6-pentakisphosphate and inositol hexakisphosphate are inhibitors of the soluble inositol 1,3,4,5-tetrakisphosphate 3-phosphatase and the inositol 1,4,5-trisphosphate/1,3,4,5-tetrakisphosphate 5-phosphatase from pig brain

Höer

Oberdisse

1991