Prevention and recovery of (mu(3)-diethylentriamino)-chloro-palladium(II)-chloride induced inhibition of Na/K-ATPase by SH containing ligands - L-cysteine and glutathione

Abstract

The effect of (mu(3)-diethylentriamino)-chloro-palladium(II)-chloride ([PdCl(dien)]Cl) on the activity of Na/K-ATPase from porcine cerebral cortex was studied in vitro, in the absence and presence of -SH containing ligandS L-cysteine and glutathione (GSH). The aim of the study was to elucidate the mechanism of [PdCl(dien)](+) induced inhibition of the enzyme activity and to examine the ability of thiols to prevent and recover the inhibition. The coordinative interaction between [PdCl(dien)](+) and enzyme was verified by UV and H-1 NMR spectra. The semblance in the changes in absorption spectra of [PdCl(dien)](+) in the presence of Na/K-ATPase and thiols (L-Cysteine and GSH) suggested that the complex ion interacts with enzymatic sulfhydryl groups. [PdCl(dien)](+) inhibited the enzyme activity in a dose-dependent manner. The Hill analysis of the inhibition curve yielded the half-maximum inhibitory activity value, IC50 = 1.21 x 10(-4) M, and Hill coefficient, n = 0.7, suggesting the negative cooperation for binding of [PdCl(dien)](+) to the enzyme. Dependence of the initial reaction rate on the concentration of MgATp(2-) exhibited typical Michelis-Menten kinetics in the absence and presence of the inhibitor. Kinetic analysis showed that [PdCl(dien)](+) inhibited Na/K-ATPase by reducing the maximum reaction rate (V-max), rather than changing the affinity to the substrate (Km). Kinetic parameters derived using Lineweaver-Burk transformation of experimental data indicated the non-competitive nature of Na/K-ATPase inhibition. The inhibitory constant, K-i = 1.05 x 10(-4) M, was determined from secondary replot of Lineweaver-Burk graph, and correlated with stability constants of [Pd(dien)(thiol)] complexes. 1 x 10(-3) M L-Cysteine or GSH prevented the enzyme inhibition induced by Pd(II) complex cation when present below 1 x 10(-4) M. The both thiols completely reversed the inhibited activity in the concentration dependent manner, due to the complex formation with [PdCl(dien)](+). (c) 2006 Elsevier Ltd. All rights reserved.