Mitochondrial adenosine triphosphatase from human placenta - inhibition by free magnesium ions of ITP hydrolysis

• Autorzy: Aleksandrowicz Z.
• Języki publikacji: EN

Abstrakty

EN

The effects of Mg2+ and bicarbonate on the kinetics of ITP hydrolysis by soluble ATPase (Fi) from human placental mitochondria were studied. Increasing amounts of Mg2+ at fixed ITP concentration, caused a marked activation of Fi followed by inhibition at higher Mg2+ concentration. The appropriate substrate for the mitochondrial Fi seems to be the MglTP complex as almost no ITP was hydrolysed in the absence of magnesium. Mg2+ behaved as a competitive inhibitor towards the MglTP complex. In this respect the human placental enzyme differ from that from other sources such as yeast, beef liver or rat liver. The linearity of the plot presenting competitive inhibition by free Mg2+ of MglTP hydrolysis (in the presence of activating bicarbonate anion) suggests that both Mg2+ and MglTP bind to the same catalytic site (Km(MgITP) = 0.46 mM, Ki(Mg) = 4 mM). When bicarbonate was absent in the ITPase assay, placental Fi exhibited apparent negative cooperativity in the presence of 5 mM Mg2+, just as it did with MgATP as a substrate under similar conditions. Bicarbonate ions eliminated the negative cooperativity with respect to ITP (as the Hill coefficient of 0.46 was brought to approx. 1), and thus limited inhibition by free Mg2+. The results presented suggest that the concentration of free magnesium ions may be an important regulatory factor of the human placental Fi activity.

Słowa kluczowe

EN

magnesium ion; mitochondrion; adenosine triphosphate synthase; human placenta; inhibitor; adenosine triphosphatase; hydrolysis

• Wydawca: -
• Czasopismo: Acta Biochimica Polonica
• Rocznik: 1994
• Tom: 41
• Numer: 1
• Opis fizyczny: p.39-44,fig.

Twórcy

autor

Aleksandrowicz Z.

• Medical Academic School, ul.Debinki 1, 80-211 Gdansk, Poland

Bibliografia

• 1. Senior, A.E. (1988) ATP synthesis by oxidative phosphorylation. Physiol. Rev. 68,177-231.
• 2. Penefsky, HS. & Cross, R.L. (1991) Structureand mechanism of FoFi-type ATP synthases and ATPases; in: Advances in Enzymology and Related Areas of Molecular Biology (Meister, A., ed.) vol. 64, pp. 173-214, John Wiley & Sons, Inc., New York.
• 3. Issartd, J.P., Dupuis, A., Garin, J., Lunardi, J., Michel, L. & Vignais, P.V. (1992) The ATP synthase (Fo-Fi) complex in oxidative phospho­rylation. Experientia 48,351-362.
• 4. Schuster, S.M., Ebel, R.E. & Lardy, H.A. (1975) Kinetic studies on rat liver and beef heart mitochondrial ATPase. Evidence for nucleotide binding at separate regulatory and catalytic sites. J. Biol. Chem. 250,784&-7853.
• 5. Grubmeyer, C. & Penefsky, H.S. (1981) The presence of two hydrolytic sites on beef heart mitochondrial adenosine triphosphatase. /. Biol. Chem. 256,3718-3727.
• 6. Cross, R.L., Grubmeyer, C. & Penefsky, H S. (1982) Mechanism of ATP hydrolysis by beef heart mitochondrial ATPases. Rate enhan­cements resulting from cooperative interactions between multiple catalytic sites. /. Biol. Chem. 257,12101-12105.
• 7. Berden, J.A., Hartog, A.F. & Edel, C.M. (1991) Hydrolysis of ATP by Fi can be described only on the basis of dual-site mechanism. Biochim. Biophys. Acta 1057,151-156.
• 8. Boyer, P.D., Cross, R.L. & Momsen, W. (1973) A new concept for energy coupling in oxidative phosphorylation based on a molecular explanation of the oxygen exchange reactions. Proc. Natl. Acad. Sci. U.S.A. 70,2837-2839.
• 9. Boyer, P.D. (1987) The unusual enzymology of ATP synthase. Biochemistry 26,8503-8507.
• 10. Boyer, P.D. (1989) A perspective of the binding change mechanism for ATP synthesis. FASEB J. 3,2164-2178.
• 11. Cross, R.L. (1988) The number of functional catalytic sites on Fi-ATPases and the effects of quarternary structural asymmetry on their properties. J. Bioenerg. Biomemhr. 20,395-405.
• 12. Cruys, K.J., Urbauer, J.L. & Schuster, S.M. (1985) Metal-nucleotide structural characteristics during catalysis by beef heart mitochonQrial Fi. /. Biol. Chem. 260, 6533-6540.
• 13. Selwyn, M.J. (1967) Preparation and general properties of a soluble adenosine triphospha­tase from mitochondria. Biochem. J. 105,279-288.
• 14. Fleury, B., Di Petro, A., Godinot, C. & Gautheron, D.C. (1980) Role of magnesium on kinetic parameters of soluble Fi-ATPase from pig heart mitochondria. Biochimie 62,733-737.
• 15. Aleksandrowicz, Z. (1980) Mitochondrial adenosine triphosphatase from human placenta Purification and catalytic properties. Int. /. Biochem. 11,165-175.
• 16. Wakagi, T. & Ohta, T. (1981) Implications of the existence of two states of beef liver mito­chondrial adenosine triphosphatase as revealed by kinetic studies. /. Biochem. (Tokyo) 89, 1205-1213.
• 17. Spector, T. (1978) Refinement of the Coomassie blue method of protein quantitation. Anal. Biochem. 86,142-146.
• 18. Ebel, R.E. & Lardy, H.A. (1975) Stimulation of rat liver mitochondrial adenosine triphosphatase by anions. /. Biol. Chem. 250,191-196.
• 19. Kayne, F.J. (1973) Pyruvate kinase; in: The Enzymes (Boyer, P.D., ed.) vol. 8, pp. 353-382, Academic Press, New York.
• 20. Adolfsen, R. & Moudrianakis, E.N. (1978) Control of complex metal ion equilibria in biochemical reaction systems. Intrinsic and apparent stability constants of metal-adenine nucleotide complexes. J. Biol. Chem. 253,4378-4379.
• 21. Pedersen, P.L. (1976) ATP-depcndent reactions catalyzed by inner membrane vesicles of rat liver mitochondria. Kinetics, substrate specificity, and bicarbonate sensitivity. J. Biol. Chem. 251,934-940.
• 22. Takeshige, K., Hess, B., Bohm, M. k Zimmerman-Telschow, H. (1976) Mitochondrial adenosine triphosphatase from yeast, Saccharomyces cerevisiae. Purification, subunit structure and kinetics. Hoppe-Seyler's Z. Physiol. Chem. 357,1605-1622.
• 23. Wong, S.-Y., Matsuno-Yagi, A. & Hatefi, Y. (1984) Kinetics of ATP hydrolysis by Fi-ATPase and the effects of anion activation, removal of tightly bound nucleotides, and partial inhibition of the ATPase by covalent modification. Biochemistry 23,5004-5009.
• 24. Rectenwald, D. & Hess, B. (1980) Classification of nucleotide binding sites on mitochondrial Fi-ATPase from yeast. Biochim. Biophys. Acta 592,377-384.
• 25. Aleksandrowicz, Z. (1985) Mitochondrial adenosine triphosphatase from human placenta. Effects of adenylyl and guanylyl imidodiphosphate. Int. J. Biochem. 17,229-234.