title: Presence of a Na+-stimulated P-type ATPase in the plasma membrane of the alkaliphilic halotolerant cyanobacterium Aphanothece halophytica.
abstract: Aphanothece cells could take up Na(+) and this uptake was strongly inhibited by the protonophore, carbonyl cyanide m-chlorophenylhydrazone (CCCP). Cells preloaded with Na(+) exhibited Na(+) extrusion ability upon energizing with glucose. Na(+) was also taken up by the plasma membranes supplied with ATP and the uptake was abolished by gramicidin D, monensin or Na(+)-ionophore. Orthovanadate and CCCP strongly inhibited Na(+) uptake, whereas N, N'-dicyclohexylcarbodiimide (DCCD) slightly inhibited the uptake. Plasma membranes could hydrolyse ATP in the presence of Na(+) but not with K(+), Ca(2+) and Li(+). The K(m) values for ATP and Na(+) were 1.66+/-0.12 and 25.0+/-1.8 mM, respectively, whereas the V(max) value was 0.66+/-0.05 mumol min(-1) mg(-1). Mg(2+) was required for ATPase activity whose optimal pH was 7.5. The ATPase was insensitive to N-ethylmaleimide, nitrate, thiocyanate, azide and ouabain, but was substantially inhibited by orthovanadate and DCCD. Amiloride, a Na(+)/H(+) antiporter inhibitor, and CCCP showed little or no effect. Gramicidin D and monensin stimulated ATPase activity. All these results suggest the existence of a P-type Na(+)-stimulated ATPase in Aphanothece halophytica. Plasma membranes from cells grown under salt stress condition showed higher ATPase activity than those from cells grown under nonstress condition.
authors.affiliation: Department of Biochemistry, Faculty of Science, Chulalongkorn University, Bangkok, Thailand.
authors.forename: Kanjana
authors.initials: K
authors.lastname: Wiangnon
authors.forename: Wuttinun
authors.initials: W
authors.lastname: Raksajit
authors.forename: Aran
authors.initials: A
authors.lastname: Incharoensakdi
mesh_terms: D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D001386:Azides / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D000458:Cyanobacteria / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D004024:Dicyclohexylcarbodiimide / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology; D006096:Gramicidin / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008094:Lithium / Q000378:metabolism; D008985:Monensin / Q000494:pharmacology; D009566:Nitrates / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology
chemical_list: D001386:Azides; D004791:Enzyme Inhibitors; D009566:Nitrates; D006096:Gramicidin; D012965:Sodium Chloride; D004024:Dicyclohexylcarbodiimide; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D010042:Ouabain; D000255:Adenosine Triphosphate; D008985:Monensin; D008094:Lithium; D012964:Sodium; D000251:Adenosine Triphosphatases; D005033:Ethylmaleimide; D011188:Potassium; D002118:Calcium