title: 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 (1)H 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, IC(50)=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 (K(m)). 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)](+).
authors.affiliation: Vinca Institute of Nuclear Sciences, Department of Physical Chemistry, P.O. Box 522, 11001 Belgrade, Serbia and Montenegro.
authors.forename: Katarina
authors.initials: K
authors.lastname: Krinulović
authors.forename: Zivadin
authors.initials: Z
authors.lastname: Bugarcić
authors.forename: Miroslav
authors.initials: M
authors.lastname: Vrvić
authors.forename: Danijela
authors.initials: D
authors.lastname: Krstić
authors.forename: Vesna
authors.initials: V
authors.lastname: Vasić
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000465:Algorithms; D000818:Animals; D000970:Antineoplastic Agents / Q000633:toxicity*; D002540:Cerebral Cortex / Q000187:drug effects / Q000201:enzymology; D003545:Cysteine / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005978:Glutathione / Q000494:pharmacology*; D007700:Kinetics; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D009942:Organometallic Compounds / Q000633:toxicity*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*; D013056:Spectrophotometry, Ultraviolet; D013552:Swine
chemical_list: C515534:(mu(3)-diethylentriamino)-chloro-palladium(II)-chloride; D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D008024:Ligands; D009942:Organometallic Compounds; D000255:Adenosine Triphosphate; D000254:Sodium-Potassium-Exchanging ATPase; D005978:Glutathione; D003545:Cysteine