Stoichiometry of ATP and metal cofactor interaction with the sarcoplasmic reticulum Ca(2+)-ATPase: a binding model accounting for radioisotopic and fluorescence results.
Sarcoplasmic reticulum Ca-ATPase belongs to the P-type ATPases family and transports calcium at the expense of ATP hydrolysis. For years, a complex pattern of activity has been observed as a function of ATP and metal cofactor concentrations, leaving the stoichiometry of both metal and ATP in the active site as an open question. In agreement with recent structural studies we present here-using Mn as analogue of Mg-radioisotopic and fluorescence results showing that two metal ions bind to the Ca-ATPase favoring ATP binding. We further show that low ATP concentration favors the binding of these ions, whereas high ATP concentration is inhibitory. We propose a binding model for ATP and metal ions, which permits simulation of our data. Finally, we suggest that (i) the contribution of two metal ions as cofactors of ATP is essential to get maximal activity; (ii) the contribution of two ATP molecules can activate or inhibit the Ca-ATPase depending on metal concentration.
González
Débora A
DA
Cátedra de Biofísica, Facultad de Odontología, Universidad de Buenos Aires, M.T. De Alvear 2142 (C1122AAH) Buenos Aires, Argentina. debora@biofis.odon.uba.ar
Ostuni
Mariano A
MA
Lacapère
Jean-Jacques
JJ
Alonso
Guillermo L
GL
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D008670:Metals / Q000378:metabolism*; D011485:Protein Binding; D011817:Rabbits; D011868:Radioisotopes; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
D008670:Metals; D011868:Radioisotopes; D000255:Adenosine Triphosphate; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases