This paper is only available as a PDF. To read, Please Download here.
An endogenous activator capable of stimulating the gastric H+,K+-ATPase activity has been purified to homogeneity from dog and pig gastric cells and found to be a dimer of two identical 40-kDa subunits in the active state. Identical nature of the activator monomers was revealed by the detection of lysine as the sole N-terminal amino acid. The activator from one species can stimulate the H+,K+-ATPase from another species and vice versa. Such cross-activation is consistent with the striking similarities in the amino acid composition between the two species, suggesting considerable homology in the activator molecules from different species. The activator exhibited several unique features during modulation of the H+,K+-ATPase reaction. It appreciably enhances affinity of the H+,K+-ATPase for K+, known to increase turnover of the enzyme. To complement this K+ affinity, the activator also enhances ability of the H+,K+-ATPase to generate more transition state (E*.ATP) complex by increasing the entropy of activation (delta S++) of the system as revealed from an Arrhenius plot of the data on temperature activation. In addition, the activator shows both positive cooperativity and strong inhibition, depending on its concentration. Thus, up to the ratio of the H+,K+-ATPase and activator of about 1:2 (on the protein basis), the activator shows sigmoidal activation (Hill coefficient = 4.5), but beyond such concentration a strong inhibition was observed. Finally, Ca2+ at low (2-4 microM) concentration strongly inhibits the activator-stimulated H+,K+-ATPase. It is proposed that the activator may be acting as a link in the signal transducing cascade system between the intracellular second messenger (Ca2+) and the physiological response (gastric H+ transport).
REFERENCES
- Annu. Rev. Physiol. 1980; 42: 111-126
- J. Surg. Res. 1981; 31: 496-505
- Gastroenterology. 1982; 198: 216-223
- Life Sci. 1983; 33: 1401-1408
- Am. J. Physiol. 1982; 242: G79-G84
- Gastroenterology. 1981; 80: 928-937
- Am. J. Physiol. 1978; 4: E546-E551
- Am. J. Physiol. 1980; 239: G90-G94
- Scand. J. Gastroenterol. 1982; 17: 533-538
- J. Biol. Chem. 1986; 261: 2660-2667
- Biochim. Biophys. Acta. 1981; 673: 539-551
- J. Biol. Chem. 1985; 260: 7540-7550
- Biochem. Biophys. Res. Commun. 1974; 61: 1199-1206
- FEBS Lett. 1978; 92: 49-52
- Biochem. J. 1983; 212: 887-890
- Arch. Biochem. Biophys. 1980; 202: 8-17
- Biochemistry. 1983; 22: 5814-5821
- Forte J.G. Warnock D.G. Rector F.C. Gastric H+ Transport in Epithelia. John Wiley & Sons, New York1984: 161-169
- Prep. Biochem. 1986; 16: 21-32
- Proc. N. Y. Acad. Sci. 1984; 435: 183-186
- Fed. Proc. 1984; 43: 2054
- Biochemistry. 1971; 10: 2606-2617
- J. Biol. Chem. 1951; 193: 265-275
- Biochem. J. 1946; 40: 628-632
- Methods Enzymol. 1967; 11: 59-62
- Methods Enzymol. 1972; 25: 121-138
- Biochem. J. 1986; 233: 231-238
- FEBS Lett. 1985; 185: 24-28
- J. Biol. Chem. 1981; 256: 7727-7729
- Biochem. Pharmacol. 1982; 31: 3103-3106
- Kasbekar D.K. Sachs G. Rehm W.S. Gastric H+ Ion Secretion. Marcel Dekker, New York1976: 187-211
- Am. J. Physiol. 1967; 212: 241-246
- Forte J.G. Warnock D.G. Rector F.C. Gastric H+ Transport in Epithelia. John Wiley & Sons, New York1984: 149-160
- Biochem. Biophys. Res. Commun. 1984; 121: 566-572
- Biochem. J. 1985; 232: 609-611
- Cyclic AMP. Academic Press, New York1971
- Nature. 1984; 311: 160-163
- Cell. 1984; 36: 577-579
- Biochemistry. 1984; 23: 2339-2352
- Stieve H. The Molecular Mechanism of Photoreception, Dahlem Konferenzen. Springer-Verlag, Berlin1986
- J. Biol. Chem. 1980; 255: 4087-4093
Article info
Publication history
Published online: April 25, 1987
Identification
Copyright
© 1987 ASBMB. Currently published by Elsevier Inc; originally published by American Society for Biochemistry and Molecular Biology.
User license
Creative Commons Attribution (CC BY 4.0) | How you can reuse
Elsevier's open access license policy

Creative Commons Attribution (CC BY 4.0)
Permitted
- Read, print & download
- Redistribute or republish the final article
- Text & data mine
- Translate the article
- Reuse portions or extracts from the article in other works
- Sell or re-use for commercial purposes
Elsevier's open access license policy