Flavonoid-Mg2+ complexes: stability, characterization, and effects on the Plasma Membrane Calcium ATPase

ONTIVEROS, MALLKU; PAVAN, CARLOS; MANGIALAVORI IRENE; ROLANDO C ROSSI; ROSSI JUAN PABLO; FERREIRA GOMES, MARIELA

BUENOS AIRES

Congreso; XLIX Reunión Anual SAB; 2021

Sociedad Argentina de Biofísica

The action of natural flavonoids as modulators of the catalytic activity of enzymes hasbeen attributed to various related chemical species, such as the formation of complexeswith metals or even oxidized forms thereof. We recently demonstrated that the flavonoidsquercetin and gossypin inhibit the Ca2+-ATPase activity of plasma membrane calciumATPase (PMCA) as a function of Mg2+ concentration, suggesting that the true inhibitor isquercetin-Mg2+ or gossypin-Mg2+. The aim of this work was to investigate the formationand stability of the quercetin-Mg2+ and gossypin-Mg2+ complexes and their effects on theinhibition of the activity of PMCA. We investigated the formation and stability of flavonoid-Mg2+ complexes using UV-Vis spectroscopy. The results show that flavonoids and theirMg2+ complexes in MOPs buffers (pH 7.4) were unstable and oxidized species wereproduced. These results are in agreement with the studies carried out by massspectrometry.On the other hand, the formation and stability of the flavonoid-Mg2+ were examined inthe same medium in which the PMCA activity was carried out. This medium contained thereagents necessary for the determination of activity, including mixed micelles of C12E10and DMPC. The results show that quercetin, gossypin, and their Mg2+ complexesremained stable without the appearance of oxidized species, suggesting that thepresence of lipids increases the stability of flavonoids.Our results show that quercetin-Mg2+ and gossypin-Mg2+ complexes were formed with astoichiometry of 1:1 and a Kd of 13.5 ± 2.7 mM and 19.6 ± 1.4 mM, respectively. On thisbasis, the Mg2+-dependent inhibition of PMCA activity was expressed as a function of theconcentrations of quercetin-Mg2+ and gossypin-Mg 2+ showing that PMCA inhibitiondepends on the concentration of the flavonoid-Mg2+ complex, suggesting that these arethe true PMCA inhibitors.AcknowldegmentsWith grants of ANPCYT, CONICET and UBACYT.