title: Inhibition of microsomal ATPases by high concentration of Mg2+ in tracheal epithelial cells.
abstract: Previous work in our laboratory established the presence of two types of microsomal ATPases, a low-affinity vanadate-sensitive (LAVS) and a high-affinity vanadate-sensitive (HAVS) ATPases, in tracheal epithelial cells. These ATPases were identified as Ca2+-ATPases by specific inhibitors and microsomal Ca2+ uptakes. Since the regulatory roles of Mg2+ on both cellular Ca2+-signaling and epithelial transports were demonstrated, the effects of Mg2+ on these ATPases were investigated. Mg2+-dependence of ATPase activity appeared bell-shaped with a maximal activity at 1-2 mM Mg2+ and Mg2+ at higher than 2 mM inhibited these enzymes. In a kinetic analysis of the LAVS ATPase inhibition, high concentration of Mg2+ appeared to inhibit the binding of ATP to a substrate-binding site. The microsomal 45Ca2+ uptakes mediated by both ATPases were also inhibited by high concentration of Mg2+. In order to test whether high concentration of Mg2+ directly inhibits these enzymes, microsomes were made leaky by the treatment of Triton X-100 and the microsomal ATPases were solubilized with CHAPS. The leaky microsomal ATPases and CHAPS-solubilized ATPases were similarly inhibited by high concentration of Mg2+, suggesting that Mg2+ directly inhibit these enzymes. In conclusion, Mg2+ has two types of modulatory effects on these enzymes, a catalytic effect at low concentration and an inhibitory effect at high concentration.
authors.affiliation: Department of Agricultural Chemistry, Chungbuk National University, Cheongju, Korea.
authors.forename: K H
authors.initials: KH
authors.lastname: Cho
authors.forename: J
authors.initials: J
authors.lastname: Sakong
authors.forename: Y K
authors.initials: YK
authors.lastname: Kim
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002793:Cholic Acids / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D008274:Magnesium / Q000494:pharmacology*; D008861:Microsomes / Q000187:drug effects* / Q000201:enzymology; D017830:Octoxynol / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D013552:Swine; D014132:Trachea / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism
chemical_list: D002793:Cholic Acids; D004791:Enzyme Inhibitors; D017830:Octoxynol; D000251:Adenosine Triphosphatases; C070990:vanadate-sensitive ATPase; D000252:Calcium-Transporting ATPases; D008274:Magnesium; C028213:3-((3-cholamidopropyl)dimethylammonium)-1-propanesulfonate