title: Specific modification of gastric K+-stimulated ATPase activity by thimerosal.
abstract: Treatment of hog gastric microsomes with the sulfhydryl reagent, thimerosal (ethylmercurithiosalicylate), produced differential effects on the K+-ATPase and the K+-stimulated p-nitrophenylphosphatase activities. For example, exposure to 2 mM thimerosal for 3 min severely reduced the activity of K+-stimulated ATPase, while K+-p-nitrophenylphosphatase activity was enhanced 2- to 3-fold. Higher concentration of thimerosal, or longer incubation times, also led to inhibition of K+-p-nitrophenylphosphatase. The activated state of p-nitrophenylphosphatase could be sustained by a 20-fold, or greater, dilution of treated membranes, and could be reversed by reduction of membrane SH groups by exogenous thiols. Significant activation of K+-p-nitrophenylphosphatase was not produced by p-chloromercuribenzene sulfonate, p-chloromercuribenzoate or mersalyl; however, ethyl mercuric chloride had qualitatively similar activity effects as thimerosal. Kinetics of K+-p-nitrophenylphosphatase for thimerosal-treated membranes were altered as follows: V increased; Km for p-nitrophenylphosphate unchanged for Ka for K+ increased. ATP, which is a potent inhibitor of K+-p-nitrophenylphosphatase activity in native membranes (KI approximately 200 microM). These data suggest that there are multiple SH groups which differentially influence the gastric K+-stimulated ATPase activity. Defined treatments with thimerosal are interpreted as an uncoupling of the K+-stimulated phosphatase component of the enzyme (for which p-nitrophenylphosphatase is a presumed model reaction). Such differential modifications can be usefully applied to the study of partial reactions of the enzyme and their specific role in the related H+-transport reaction.
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D027682:Cation Transport Proteins; D005035:Ethylmercury Compounds / Q000494:pharmacology*; D005753:Gastric Mucosa / Q000201:enzymology*; D007425:Intracellular Membranes / Q000201:enzymology; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology; D013552:Swine; D013849:Thimerosal / Q000494:pharmacology*
chemical_list: D027682:Cation Transport Proteins; D005035:Ethylmercury Compounds; D013849:Thimerosal; D009597:4-Nitrophenylphosphatase; D000251:Adenosine Triphosphatases; C022761:potassium transporting ATPase