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J Bacteriol. 1969 November; 100(2): 914-922
Copyright © 1969 American Society for Microbiology. All Rights Reserved.

Membrane Adenosine Triphosphatase of Escherichia coli: Activation by Calcium Ion and Inhibition by Monovalent Cations¹

^a Dental Research Department, Naval Medical Research Institute, Bethesda, Maryland 20014

ABSTRACT

Membrane ghost preparations of Escherichia coli K-12 obtained by osmotic lysis of lysozyme-induced spheroplasts were found to possess both Mg⁺⁺- and Ca⁺⁺-activated adenosine 5'-triphosphatase (ATPase, EC 3.6.1.3) activities. Maximal activities of 1.0 to 1.5 µmoles of orthophosphate released per min per mg of protein were obtained at pH 9.0 with a molar Mg⁺⁺ to adenosine 5'triphosphate (ATP) ratio of 2:5 and at pH 9.9 with a molar Ca⁺⁺ to ATP ratio of 1:5. These ATPase activities were not altered by ouabain, fluoride, N-ethylmaleimide, 2,4-dinitrophenol, cyanide, or dithionite, but were inhibited by low concentrations of azide, p-chloromercuribenzoate, and pentachlorophenol. Mg⁺⁺ ATPase was more susceptible to inhibition by azide than was Ca⁺⁺ ATPase. Fifty per cent inactivation of both activities was observed when membrane ghost preparations were preincubated at 66 C for 10 min. The Mg⁺⁺ and Ca⁺⁺ ATPase activities of these preparations were not additive, but did respond independently to inhibition by monovalent cations. Ca⁺⁺ ATPase was found to be very sensitive to inhibition by K⁺, Na⁺, Li⁺, Rb⁺, and Cs⁺; Mg⁺⁺ ATPase was relatively insensitive to these ions. One possible interpretation of the results presented in this paper is that the membrane of E. coli possesses an ATPase which is activated by either Mg⁺⁺ or Ca⁺⁺ and that activation by Ca⁺⁺ increases the susceptibility of this enzyme to inhibition by monovalent cations. Increased susceptibility of E. coli membrane ATPase to inhibition by monovalent cations such as Na⁺ and K⁺ as a consequence of Ca⁺⁺ activation could represent a regulatory mechanism.

² NRC-Bureau of Medicine and Surgery, Department of Navy, Postdoctoral Research Associate.

¹ From the Bureau of Medicine and Surgery, Department of Navy, Research Task MF12 524 009 1006.

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