Dataset Information

Reaction mechanism of the gastric H+ +K+-dependent ATPase. Effects of inhibitor and pH.

ABSTRACT: The effect of nolinium bromide [2-(3,4-dichlorophenylamino)quinolizium bromide], which acts as a K+ antagonist in the gastric H+ +K+-dependent ATPase reaction, was investigated at the level of 32P-labelled intermediates of the gastric ATPase reaction. A concentration-dependent effect of nolinium bromide was observed on the concentrations of phosphorylated intermediates. At low (up to 50 microM) concentrations the drug did not interfere with the concentrations of intermediates but exhibited a competition with K+ at the level of both 32P-labelled intermediates and hydrolysis of ATP at pH 7.0. Similar competition was noted in the H+ +K+-dependent ATPase reaction. Low nolinium bromide concentrations also drastically slowed the enzyme turnover. The concentrations of the intermediates were lowered appreciably between 50 microM- and 100 microM-nolinium bromide without affecting the ATP hydrolysis, and the effects were independent of pH. Similar to the effects at pH 7.0, the drug also exhibited competition with K+ in lowering the E approximately P concentration at pH 5.0. A dramatic effect of pH on the K+-sensitivity as well as on turnover of the 32P-labelled intermediates was observed. Although the concentrations of intermediates remained nearly unaltered at various pH values, the K+-stimulated hydrolysis of ATP showed an optimum at pH 7.0 with sharp declines at pH 5 and 8. The data suggest a critical involvement of H+ in the conversion of the K+-insensitive E1 approximately P into the K+-sensitive E2 approximately P form of the enzyme. Nolinium bromide appears to function as a K+ analogue and seems to block the entry of K+ at the K X E2 step, thereby interfering with the enzyme turnover.

SUBMITTER: Nandi J

PROVIDER: S-EPMC1147540 | biostudies-other | 1987 Jan

REPOSITORIES: biostudies-other

ACCESS DATA

Similar Datasets

Project description:Gastric H,K-ATPase is an electroneutral transmembrane pump that moves protons from the cytoplasm of the parietal cell into the gastric lumen in exchange for potassium ions. The mechanism of transport against the established electrochemical gradients includes intermediate conformations in which the transferred ions are trapped (occluded) within the membrane domain of the pump. The pump cycle involves switching between the E1 and E2P states. Molecular dynamics simulations on homology models of the E2P and E1 states were performed to investigate the mechanism of K(+) movement in this enzyme. We performed separate E2P simulations with one K(+) in the luminal channel, one K(+) ion in the occlusion site, two K(+) ions in the occlusion site, and targeted molecular dynamics from E2P to E1 with two K(+) ions in the occlusion site. The models were inserted into a lipid bilayer system and were stable over the time course of the simulations, and K(+) ions in the channel moved to a consistent location near the center of the membrane domain, thus defining the occlusion site. The backbone carbonyl oxygen from residues 337 through 342 on the nonhelical turn of M4, as well as side-chain oxygen from E343, E795, and E820, participated in the ion occlusion. A single water molecule was stably bound between the two K(+) ions in the occlusion site, providing an additional ligand and partial shielding the positive charges from one another. Targeted molecular dynamics was used to transform the protein from the E2P to the E1 state (two K(+) ions to the cytoplasm). This simulation identified the separation of the water column in the entry channel as the likely gating mechanism on the luminal side. A hydrated exit channel also formed on the cytoplasmic side of the occlusion site during this simulation. Hence, water molecules became available to hydrate the ions. The movement of the M1M2 transmembrane segments, and the displacement of residues Q159, E160, Q110, and T152 during the conformational change, as well as the motions of E343 and L346, acted as the cytoplasmic-side gate.

Project description:Background:Proton pump inhibitor (PPI) and other acid-suppressing drugs are widely used in the treatment of gastrointestinal ulcer, upper gastrointestinal bleeding, gastritis, and gastric cancer (GC). About 80% of GC patients receive acid suppression treatment. PPI suppresses the production of gastric acid by inhibiting the function of H+/K+-ATPase in gastric parietal cells and raises the pH value to achieve therapeutic purposes. Some studies have found that PPI had a certain antitumor effect in the proliferation and apoptosis of tumor cells. But the effects of environmental pH on the growth of GC cells and its mechanism are unknown. Therefore, we hoped to find the effects of culture medium pH on the biological behavior of GC cells by in vitro experiments and provide guidance for the use of acid-suppressing drugs in GC patients. Aims:We aimed to observe the effects of pH changes in GC cell culture medium on the cell biological behavior of cancer cells and to analyze the potential mechanisms. We hoped to find out the effect of acid suppression on the growth of GC cells. Methods:The GC cell lines (SGC-7901 and MKN45) were used as the research object. We adjusted the pH value in the cell culture medium to observe the changes in cell viability (MTT), apoptosis (flow cytometry), and invasion (Transwell) at pH?6, pH?7, and pH?8. qRT-PCR and western blot (WB) assays were used to determine the expression changes of genes and proteins (mTOR, AKT, Wnt, Glut, and HIF-1?) at pH?6, pH?7, and pH?8. Results:The results of MTT showed that the viability of SGC-7901 and MKN45 in the pH?8.0 group was significantly weaker than that in the pH?6.0 or pH?7.0 group (P < 0.001). Flow cytometry results showed that the apoptosis of SGC-7901 and MKN45 in the pH?8.0 group was more obvious than that in the pH?6.0 or pH?7.0 group (P < 0.001). Flow cytometry results showed that the apoptosis of SGC-7901 and MKN45 in the pH?8.0 group was more obvious than that in the pH?6.0 or pH?7.0 group (P < 0.001). Flow cytometry results showed that the apoptosis of SGC-7901 and MKN45 in the pH?8.0 group was more obvious than that in the pH?6.0 or pH?7.0 group (?) at pH?6, pH?7, and pH?8. P < 0.001). Flow cytometry results showed that the apoptosis of SGC-7901 and MKN45 in the pH?8.0 group was more obvious than that in the pH?6.0 or pH?7.0 group (. Conclusions:Compared with the microacid environment, the microalkaline environment inhibited the viability, invasion, and expression of genes and proteins (mTOR, AKT, Wnt, Glut, and HIF-1?) but promoted the apoptosis of GC cells and thus inhibited the growth of GC.?) at pH?6, pH?7, and pH?8.

Dataset Information

Reaction mechanism of the gastric H+ +K+-dependent ATPase. Effects of inhibitor and pH.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets