Interaction of some Pd(II) complexes with Na+/K+-ATPase: Inhibition,kinetics, prevention and recovery

The aim of this work was to investigate the influence of [PdCl₄]^{2 ?} , [PdCl(dien)]⁺ and [PdCl(Me₄dien)]⁺ complexes on Na⁺/K⁺-ATPase activity. The dose-dependent inhibition curves were obtained in all cases. IC₅₀ values determined by Hill analysis were 2.25 × 10^{? 5} M, 1.21 × 10^{? 4} M and 2.36 × 10^{? 4} M, respectively. Na⁺/K⁺-ATPase exhibited typical Michelis-Menten kinetics in the presence of Pd(II) complexes. Kinetic parameters (V_max, K_m) derived using Eadie–Hofstee transformation indicated a noncompetitive type of Na⁺/K⁺-ATPase inhibition. The inhibitor constants (K_i) were determined from Dixon plots. The order of complex affinity for binding with Na⁺/K⁺-ATPase, deducted from K_i values, was [PdCl₄]^{2 ?} >[PdCl(dien)]⁺>[PdCl(Me₄dien)]⁺. The results indicated that the potency of Pd(II) complexes to inhibit Na⁺/K⁺-ATPase activity depended strongly on ligands of the related compound. Furthermore, the ability of SH-donor ligands, l-cysteine and glutathione, to prevent and recover the Pd(II) complexes-induced inhibition of Na⁺/K⁺-ATPase was examined. The addition of 1 mM l-cysteine or glutathione to the reaction mixture before exposure to Pd(II) complexes prevented the inhibition by increasing the IC₅₀ values by one order of magnitude. Moreover, the inhibited enzymatic activity was recovered by addition of SH-donor ligands in a concentration-dependent manner.