title: Characterization of a calcium-dependent ATPase in Entamoeba invadens.
abstract: A high-affinity calcium-dependent ATPase (Ca2+-ATPase) was identified in a crude plasma membrane fraction from Entamoeba invadens (IP-1 strain). The Ca2+-ATPase activity was solubilized from the membrane by utilizing the non-ionic detergent octylglucoside. The activity had an apparent half maximal saturation constant of 0.4 +/- 0.05 microM for free calcium. The calcium activation of ATPase activity followed a cooperative mechanism (Hill number of 2.3 +/- 0.13) which suggests that two interacting sites were involved. The high-affinity Ca2+-ATPase appeared to be magnesium-independent, since by lowering contaminant free magnesium with trans-cyclohexane-1,2-diamine-N,N,N',N'-tetraacetic acid did not modify the activity observed with Ca2+. The apparent Km of the enzyme for ATP was 31 microM. The observed activity had an optimum pH of 8.8. The enzyme was insensitive to various agents such as Na+, K+, ouabain, dicyclohexylcarbodiimide, KCN, NaN3, mersalyl, quercetin, ruthenium red and vanadate. Only lanthanum (0.5 mM) inhibited 100% the enzymatic activity. Calmodulin and trifluoperazine at the concentrations tested did not modify the Ca2+-ATPase activity.
authors.forename: A
authors.initials: A
authors.lastname: Zarain-Herzberg
authors.forename: A
authors.initials: A
authors.lastname: Arroyo-Begovich
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002147:Calmodulin / Q000494:pharmacology; D002462:Cell Membrane / Q000201:enzymology; D004533:Egtazic Acid; D004747:Entamoeba / Q000201:enzymology*; D005960:Glucosides / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000494:pharmacology; D017830:Octoxynol; D011092:Polyethylene Glycols / Q000494:pharmacology; D012995:Solubility
chemical_list: D002147:Calmodulin; D005960:Glucosides; C018619:octyl-beta-D-glucoside; D011092:Polyethylene Glycols; D004533:Egtazic Acid; D000255:Adenosine Triphosphate; D017830:Octoxynol; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D002118:Calcium