IQUIFIB   02644
INSTITUTO DE QUIMICA Y FISICOQUIMICA BIOLOGICAS "PROF. ALEJANDRO C. PALADINI"
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
A model for the interaction between Rb+, ATP and Na+/K+-ATPase
Autor/es:
ALEJANDRO J. SPIAGGI; MÓNICA R. MONTES; RODOLFO M. GONZÁLEZ-LEBRERO; ROLANDO C. ROSSI
Lugar:
Salta
Reunión:
Congreso; 3rd Latin American Protein Society Meeting - XXXIX Reunión Anual de la Sociedad Argentina de Biofisica; 2010
Resumen:
Occlusion of K+ (or its congeners Rb+ or Tl+) in the Na+/K+-ATPase occurs after K+-dependent dephosphorylation (“physiological route”) or through a “direct route” not related to ATPase activity.  Our results indicate that: i) occlusion of Rb+ through the direct route, as well as its release from the occluded states, are at least two-steps processes that can be described by the sum of two exponential functions of time, for every [Rb+] and [ATP] tested; ii) the fraction of Rb+ that is occluded or released in the faster phase is enlarged by ATP; iii) the initial rate of occlusion is directly proportional to free [Rb+] up to 250 mM in the absence of ATP, whereas it decreases with [ATP] and becomes an increasing sigmoidal function of free [Rb+] at [ATP] = 2000 mM; iv) the nucleotide markedly increases the initial rate and the rate coefficients of both phases of Rb+ deocclusion; v) at equilibrium, the direct route results in enzyme states that hold either one or two occluded Rb+ ions even in enzymes with ATP bound; vi) equilibrium between bound and occluded Rb+ seems to be almost completely poised towards the latter in spite of the mentioned effect of ATP on occlusion and deocclusion rates. Part of these results had been previously observed in our lab1,2. The kinetics of Rb+ occlusion and deocclusion through the direct route in the presence of ATP are consistent with a model that assumes that: 1) these processes can follow two alternative and interrelated pathways associated with the conformers E1 and E2; 2) only E2 can occlude Rb+; 3) uptake or release of each cation involves an ordered-sequential process; and 4) ATP can bind to E1 and E2, being its affinity for E1 much higher. References: 1. González-Lebrero R. M., Kaufman S. B., Montes M. R., Nørby J. G., Garrahan P. J. and Rossi, R. C., J. Biol. Chem., 277, 5910 – 5921 (2002) 2. González-Lebrero R. M., Kaufman S. B., Garrahan P. J. and Rossi, R. C., J. Biol. Chem., 277, 5922 – 5928 (2002) With grants from ANPCyT, CONICET and Universidad de Buenos Aires.