ABSTRACT
The mechanism of the vanadate (V(V]-dependent oxidation of NADH was different in phosphate buffers and in phosphate-free media. In phosphate-free media (aqueous medium or HEPES buffer) the vanadyl (V(IV] generated by the direct V(V)-dependent oxidation of NADH formed a complex with V(V). In phosphate buffers V(IV) autoxidized instead of forming a complex with V(V). The generated superoxide radical (O2-) initiated, in turn, a high-rate free radical chain oxidation of NADH. Phosphate did not stimulate the V(V)-dependent NADH oxidation catalyzed by O2--generating systems. Monovanadate proved to be a stronger catalyzer of NADH oxidation as compared to polyvanadate.
Subject(s)
NAD/metabolism , Oxidation-Reduction/drug effects , Vanadates/pharmacology , Hydrogen-Ion Concentration , Kinetics , Phosphates/pharmacology , Spectrophotometry , Spectrophotometry, Ultraviolet , Superoxide Dismutase/metabolismABSTRACT
Aspirin and indomethacin decreased the hydrolysis of microsomal phospholipids by exogenous soluble phospholipase A2 and increased lipid peroxidation in rat liver microsomes. Copper chelates of the non-steroidal anti-inflammatory drugs tested more strongly decreased the activity of soluble phospholipase A2 as compared to the ligands. In contrast to the stimulant effects of aspirin and indomethacin these chelates exerted dose-dependent inhibitory effects on enzymatic and non-enzymatic lipid peroxidation. The effects of CuSO4 were similar to those of Cu(II)-aspirin and Cu(II)-indomethacin. Bathocuproine sulfonate, a specific chelator for Cu+, completely prevented the inhibitory effects of copper complexes and of CuSO4 both on lipid peroxidation and on microsomal NADPH-oxidation. Therefore, cupric ions, free or chelated, as well as their reduction to Cu+ by microsomes did not affect the activity of NADPH-dependent cytochrome P-450 reductase. These data are explained by drug-induced changes in the membrane structure as well as by the redox cycling of cupric ions in the copper complexes of aspirin and indomethacin and the subsequent and/or simultaneous interaction of Cu2+/Cu+ with some component(s) of the reaction medium.