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Limited tryptic digestion of fluorescein isothiocyanate (FITC)-labeled (H+-K+)-ATPase from rat resting light gastric membranes produced a soluble 27-kDa polypeptide which retained the fluorescence of the parent enzyme. Its production was markedly enhanced in the presence of an amphiphilic detergent, Zwittergent 3-14, which potently inhibits the ATPase activity. This increase is probably due to protection of certain tryptic cleavage sites through conformational changes of the membrane enzyme by the detergent. The NH2-terminal sequence of the 27-kDa polypeptide corresponded exactly to that beginning at Asn-369 of the cDNA-deduced primary structure of the rat ATPase. The presence of the phosphorylation site, Asp-385, and FITC-labeled Lys-517, which is known to be a part of the ATP-binding site, indicates that the 27-kDa polypeptide contains a major cytoplasmic portion of (H+-K+)-ATPase. Interestingly, the polypeptide was stained with periodate-Schiff's base, indicating its glycoprotein nature. The carbohydrate group attached to the polypeptide seems to include at least an N-linked high-mannose moiety, since the polypeptide showed Con A binding activity as detected with a Con A-biotin/avidin-peroxidase assay on nitrocellulose transblots. Also, its Con A binding activity was inhibited by excess methyl alpha-D-mannopyranoside and disappeared upon treatment of the polypeptide with endoglycosidase H and N-glycanase. Further tryptic action converted the 27-kDa polypeptide to 2 smaller FITC-labeled polypeptides of 25 and 15 kDa, which lost 18 and 96 amino acid residues, respectively, from the NH2 terminus of the parent polypeptide.(ABSTRACT TRUNCATED AT 250 WORDS)

The synthesis of N-substituted benzimidazole (H(+)-K+)-ATPase or proton-pump inhibitors is described. These compounds were prepared to function as prodrugs of the parent N-H compound and evaluated for their ability to inhibit gastric (H(+)-K+)-ATPase and gastric acid secretion. The prodrugs reported rely on either in vivo esterase hydrolysis for liberation of the parent compound (type I and type II) or require an acid environment for release of the active drug (type III and type IV). The N-(acyloxy)alkyl-substituted benzimidazoles 9, 11, and 24 showed improved chemical stability in the solid state and in aqueous solutions when compared to their parent N-H compounds. When given orally, 24 was found to be twice as potent as omeprazole in both the Shay rat and inactivation of gastric (H(+)-K+)-ATPase in the rat. The N-ethoxy-1-ethyl-substituted benzimidazoles 48-50 were found equally as effective as the N-H compound for inhibition of rat (H(+)-K+)-ATPase activity. In the Shay rat 48 at 10 mg/kg was approximately twice as active as parent timoprazole.