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 Ca 2+-ATPases by specific inhibitors and microsomal Ca 2+ uptakes. Since the regulatory roles of Mg 2+ on both cellular Ca 2+-signaling and epithelial transports were demonstrated, the effects of Mg 2+ on these ATPases were investigated. Mg 2+-dependence of ATPase activity appeared bell-shaped with a maximal activity at 1–2 mM Mg 2+ and Mg 2+ at higher than 2 mM inhibited these enzymes. In a kinetic analysis of the LAVS ATPase inhibition, high concentration of Mg 2+ appeared to inhibit the binding of ATP to a substrate-binding site. The microsomal 45Ca 2+ uptakes mediated by both ATPases were also inhibited by high concentration of Mg 2+. In order to test whether high concentration of Mg 2+ 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 Mg 2+, suggesting that Mg 2+ directly inhibit these enzymes. In conclusion, Mg 2+ has two types of modulatory effects on these enzymes, a catalytic effect at low concentration and an inhibitory effect at high concentration.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call