Phosphoinositide kinases in rat heart sarcolemma

biochemical properties and regulation by calcium

Nasrin Mesaeli, Jos M J Lamers, Vincenzo Panagia

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

Phosphatidylinositol (PtdIns) kinase and phosphatidylinositol 4-phosphate (PtdIns4P) kinase have been studied in a purified sarcolemmal fraction isolated from rat heart. Both enzymes were Mg2--dependent and their activities were maximal at 2.5 mM Mg2+ and pH 7.5. Kinetic analysis of endogenous substrate phosphorylation by ATP showed that the apparent Km and Vmax values for PtdIns kinase were 292 ± 17 μM and 1390 ± 80 pmol · mg-1 · min-1, respectively, while the apparent Km and Vmax values for PtdIns4P kinase were 398 ± 25 μM and 382 ± 24 pmol · mg-1 · min-1. Under normal conditions, the activity of PtdIns4P kinase was lower than that of PtdIns kinase; however, the former activity increased several fold in the presence of PtdIns4P as an exogenous substrate. The enzymatic synthesis of intramembranal PtdIns4P and phosphatidylinositol 4,5-bisphosphate (PtdIns (4,5)P2) was maximally enhanced by 0.1% Triton X-100 and inhibited by micromolar concentrations of Ca2-. Inhibition of PtdIns and PtdIns4P kinase showed IC50 values for Ca2+ of 20 and 6 μM, respectively, and was independent of either Ca2+-induced activation of phospholipase C and polyphosphoinositide monophosphoesterases or low ATP concentrations. The results indicate that purified rat heart sarcolemmal membranes contain a very active phosphoinositide phosphorylation system which is regulated by micromolar levels of Ca2-. The Ca2+ effect may contribute to the feedback inhibition of the receptor-activated formation of inositol 1,4,5-trisphosphate.

Original languageEnglish
Pages (from-to)181-189
Number of pages9
JournalMolecular and Cellular Biochemistry
Volume117
Issue number2
DOIs
Publication statusPublished - Nov 1992
Externally publishedYes

Fingerprint

Sarcolemma
1-Phosphatidylinositol 4-Kinase
Phosphatidylinositols
Rats
Calcium
Phosphorylation
Phosphotransferases
Adenosine Triphosphate
Phosphoinositide Phospholipase C
Inositol 1,4,5-Trisphosphate
Octoxynol
Substrates
Inhibitory Concentration 50
Chemical activation
Membranes
Feedback
Kinetics
1-phosphatidylinositol-4-phosphate 5-kinase
Enzymes

Keywords

  • Ca
  • phosphoinositide kinases
  • polyphosphoinositides
  • rat heart
  • sarcolemma

ASJC Scopus subject areas

  • Molecular Biology
  • Genetics
  • Clinical Biochemistry
  • Cell Biology

Cite this

Phosphoinositide kinases in rat heart sarcolemma : biochemical properties and regulation by calcium. / Mesaeli, Nasrin; Lamers, Jos M J; Panagia, Vincenzo.

In: Molecular and Cellular Biochemistry, Vol. 117, No. 2, 11.1992, p. 181-189.

Research output: Contribution to journalArticle

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abstract = "Phosphatidylinositol (PtdIns) kinase and phosphatidylinositol 4-phosphate (PtdIns4P) kinase have been studied in a purified sarcolemmal fraction isolated from rat heart. Both enzymes were Mg2--dependent and their activities were maximal at 2.5 mM Mg2+ and pH 7.5. Kinetic analysis of endogenous substrate phosphorylation by ATP showed that the apparent Km and Vmax values for PtdIns kinase were 292 ± 17 μM and 1390 ± 80 pmol · mg-1 · min-1, respectively, while the apparent Km and Vmax values for PtdIns4P kinase were 398 ± 25 μM and 382 ± 24 pmol · mg-1 · min-1. Under normal conditions, the activity of PtdIns4P kinase was lower than that of PtdIns kinase; however, the former activity increased several fold in the presence of PtdIns4P as an exogenous substrate. The enzymatic synthesis of intramembranal PtdIns4P and phosphatidylinositol 4,5-bisphosphate (PtdIns (4,5)P2) was maximally enhanced by 0.1{\%} Triton X-100 and inhibited by micromolar concentrations of Ca2-. Inhibition of PtdIns and PtdIns4P kinase showed IC50 values for Ca2+ of 20 and 6 μM, respectively, and was independent of either Ca2+-induced activation of phospholipase C and polyphosphoinositide monophosphoesterases or low ATP concentrations. The results indicate that purified rat heart sarcolemmal membranes contain a very active phosphoinositide phosphorylation system which is regulated by micromolar levels of Ca2-. The Ca2+ effect may contribute to the feedback inhibition of the receptor-activated formation of inositol 1,4,5-trisphosphate.",
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