Localization and cation dependence of a Ca2+- or Mg2+-ATPase from electrocytes of Electrophorus electricus, L

Electrocyte membranes of Electrophorus electricus exhibit high ATPase activity, as demonstrated by cytochemical and biochemical techniques. This activity is visualized as electron-dense deposits in electron micrographs, and appears to be localized only at the innervated face of the electrocyte. ATP...

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Bibliographic Details
Published in:The journal of histochemistry and cytochemistry 1989-07, Vol.37 (7), p.953-959
Main Authors: Taffarel, M, Coelho-Sampaio, T, Teixeira-Ferreira, A, Somlo, C, De Souza, W, Machado, RD, Vieyra, A
Format: Article
Language:English
Subjects:
Adenosine Triphosphate - metabolism
Adenosine Triphosphate - pharmacology
Animals
Ca(2+) Mg(2+)-ATPase - metabolism
Calcium Chloride - pharmacology
Calcium-Transporting ATPases - metabolism
Cations, Divalent
Cell Membrane - enzymology
Electric Organ - enzymology
Electric Organ - ultrastructure
Electrophorus - metabolism
Histocytochemistry
Hydrogen-Ion Concentration
Hydrolysis
Magnesium - pharmacology
Magnesium Chloride
Microscopy, Electron
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Summary:Electrocyte membranes of Electrophorus electricus exhibit high ATPase activity, as demonstrated by cytochemical and biochemical techniques. This activity is visualized as electron-dense deposits in electron micrographs, and appears to be localized only at the innervated face of the electrocyte. ATP hydrolysis can be detected cytochemically or biochemically only in the presence of calcium or magnesium. The effects of Ca or Mg on ATPase activity can be described by Michaelis-like functions with similar apparent Km values for Ca and Mg (0.41 mM and 0.23 mM, respectively). Vmax, however, is fivefold higher in the presence of Mg. The effects of the two cations are not additive, and pH dependence of ATP hydrolysis is identical in the presence of Ca or Mg (maximal at pH 8-9). Therefore, it can be concluded that Ca and Mg activate the same enzyme, the differences in Vmax being attributable to influences in kcat.
ISSN:0022-1554
1551-5044
DOI:10.1177/37.7.2525141