Phosphoinositide kinases in rat heart sarcolemma: biochemical properties and regulation by calcium

Nasrin Mesaeli, Jos M J Lamers, Vincenzo Panagia

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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
Issue number2
Publication statusPublished - Nov 1992
Externally publishedYes



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

ASJC Scopus subject areas

  • Molecular Biology
  • Genetics
  • Clinical Biochemistry
  • Cell Biology

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