title: The effect of di- and trivalent cations on the phosphorylation of the Ca2+-ATPase in sarcoplasmic reticulum vesicles.
abstract: The steady-state level of phosphorylated intermediate (EP) of (Mg2+ + Ca2+)-ATPase is influenced by magnesium and calcium concentration in the Ca2+-transporting system of sarcoplasmic reticulum vesicles. At micromolar [Ca2+], the level of EP is increased by Mg2+, depending on its concentration. The effect of Mg2+ is less pronounced at lower Ca2+ concentration. At low [Mg2+], the EP formation increases at millimolar concentrations of Ca2+, suggesting, in accordance with earlier results, that the substrate may also be CaATP instead of MgATP. LaCl3 (1 mM) enhanced the EP formation at low Mg2+ concentration. Surprisingly, 10 microM LaCl3 caused a marked decrease in EP formation at high [Mg2+] and had little or no effect on the level of EP at low Mg2+ concentration. The inducing effect of 1 mM LaCl3 on the EP formation at low [Mg2+] and the inhibitory effect of 10 microM LaCl3 at high Mg2+ concentration draw attention to the involvement of divalent cation-binding sites with different affinity in phosphorylation and to the particular role of Mg2+ in the EP formation and EP decomposition.
authors.forename: J
authors.initials: J
authors.lastname: Domonkos
authors.forename: L
authors.initials: L
authors.lastname: Heiner
authors.forename: M
authors.initials: M
authors.lastname: Vargha
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002412:Cations; D002413:Cations, Divalent; D019811:Hydroxylamine; D006898:Hydroxylamines / Q000494:pharmacology; D007700:Kinetics; D007811:Lanthanum / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D009132:Muscles / Q000201:enzymology; D010766:Phosphorylation; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*
chemical_list: D002412:Cations; D002413:Cations, Divalent; D006898:Hydroxylamines; D019811:Hydroxylamine; D007811:Lanthanum; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D002118:Calcium