Calcium uptake and proton transport by acidocalcisomes of Toxoplasma gondii

PLoS One. 2011 Apr 25;6(4):e18390. doi: 10.1371/journal.pone.0018390.


Acidocalcisomes are acidic calcium stores found in diverse organisms, being conserved from bacteria to humans. They possess an acidic matrix that contains several cations bound to phosphates, which are mainly present in the form of short and long polyphosphate chains. Their matrix is acidified through the action of proton pumps such as a vacuolar proton ATPase and a vacuolar proton pyrophosphatase. Calcium uptake occurs through a Ca(2+)/H(+) countertransporting ATPase located in the membrane of the organelle. Acidocalcisomes have been identified in a variety of microorganisms, including Apicomplexan parasites such as Plasmodium and Eimeria species, and in Toxoplasma gondii. We report the purification and characterization of an acidocalcisome fraction from T. gondii tachyzoites after subcellular fractionation and further discontinuous iodixanol gradient purification. Proton and calcium transport activities in the fraction were characterized by fluorescence microscopy and spectrophotometric methods using acridine orange and arsenazo III, respectively. This work will facilitate the understanding of the function of acidocalcisomes in Apicomplexan parasites, as we can now isolate highly purified fractions that could be used for proteomic analysis to find proteins that may clarify the biogenesis of these organelles.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate / metabolism
  • Biomarkers / metabolism
  • Calcium / metabolism*
  • Calcium Chloride / pharmacology
  • Cell Membrane Permeability / drug effects
  • Ion Transport / drug effects
  • Organelles / drug effects
  • Organelles / metabolism*
  • Organelles / ultrastructure
  • Polyphosphates / metabolism
  • Proton Pumps / metabolism
  • Protons*
  • Sodium Chloride / pharmacology
  • Subcellular Fractions / drug effects
  • Subcellular Fractions / metabolism
  • Toxoplasma / cytology
  • Toxoplasma / drug effects
  • Toxoplasma / metabolism*
  • Triiodobenzoic Acids / pharmacology


  • Biomarkers
  • Polyphosphates
  • Proton Pumps
  • Protons
  • Triiodobenzoic Acids
  • Sodium Chloride
  • Adenosine Triphosphate
  • iodixanol
  • Calcium Chloride
  • Calcium