Interaction of terbium ions with inorganic pyrophosphatase from bakers' yeast: characterization of the binding sites
Hansen, G.; Höhne, W.E.; Kuranova, I.P.
Acta Biologica et Medica Germanica 41(1): 23-30
1982
ISSN/ISBN: 0001-5318 PMID: 6126058 Document Number: 184875
Terbium ions bind with a 2:1 stoichiometry per subunit to inorganic pyrophosphatase from bakers' yeast (EC 3.6.1.1) as measured by an increase of terbium fluorescence. The Tb3+ inhibition of the Mg2+ activated pyrophosphate hydrolysis is caused by a competitive binding at the substrate site of the active centre. The second Mg2+ binding site--the so-called "stabilization site"--is discussed as an additional binding site for Tb3+. Thereby, Tb3+ causes also a stabilization of the enzyme against heat denaturation. The dissociation constants of the terbium-pyrophosphatase interaction are in the micromolar range.