Effect of cadmium on ferredoxin:NADP+ oxidoreductase activity (original) (raw)
Related papers
Ferredoxin: NADP+ oxidoreductase as a target of Cd2+ inhibitory action-Biochemical studies
2010
The ferredoxin:NADP+ oxidoreductase (FNR) catalyses the ferredoxin-dependent reduction of NADP+ to NADPH in linear photosynthetic electron transport. The enzyme also transfers electrons from reduced ferredoxin (Fd) or NADPH to the cytochrome b 6 f complex in cyclic electron transport. In vitro, the enzyme catalyses the NADPH-dependent reduction of various substrates, including ferredoxin, the analogue of its redox centre -ferricyanide, and the analogue of quinones, which is dibromothymoquinone. This paper presents results on the cadmium-induced inhibition of FNR. The K i value calculated for research condition was 1.72 mM.
Cadmium-Dependent Enzyme Activity Alteration Is Not Imputable to Lipid Peroxidation
Archives of Biochemistry and Biophysics, 2000
The effect of cadmium on the liver-specific activities of NADPH-cytochrome P450 reductase (CPR), malic dehydrogenase (MDH), glyceraldehyde-3-phosphate dehydrogenase (GADPH), and sorbitol dehydrogenase (SDH) was assessed 6, 24, and 48 h after administration of the metal to rats (2.5 mg/kg of body weight, as CdCl 2 , single ip injection). CPR specific activity increased after 6 h and afterward decreased significantly, while MDH specific activity increased up to 24 h and then remained unchanged. Both SDH and GADPH specific activities reduced after 6 h, the former only a little but the latter much more, and after 24 and 48 h were strongly inhibited. In vitro experiments, by incubating rat liver microsomes, mitochondria, or cytosol with CdCl 2 in the pH range 6.0 -8.0, excluded cadmium-induced lipid peroxidation as the cause of the reduction in enzyme activity. In addition, from these experiments, we obtained indications on the type of interactions between cadmium and the enzymes studied. In the case of CPR, the inhibitory effect is probably due to Cd 2؉ binding to the histidine residue of the apoenzyme, which, at physiological pH, acts as a nucleophilic group. In vitro, mitochondrial MDH was not significantly affected by cadmium at any pH, indicating that this enzyme is probably not involved in the decrease in mitochondrial respiration caused by this metal. As for GADPH specific activity, its inhibition at pH 7.4 and above is imputable to the binding of cadmium to the SH groups present in the enzyme active site, since in the presence of dithiothreitol this inhibition was removed. SDH was subjected to a dual effect when cytosol was exposed to cadmium. At pH 6.0 and 6.5, its activity was strongly stimulated up to 75 M CdCl 2 while at higher metal concentrations it was reduced. At pH 7.4 and 8.0, a stimulation up to 50 M CdCl 2 occurred but above this concentration, a reduc-tion was found. These data seem to indicate that cadmium can bind to different enzyme sites. One, at low cadmium concentration, stimulates the SDH activity while the other, at higher metal concentrations, substitutes for zinc, thus causing inhibition. This last possibility seems to occur in vivo essentially at least 24 h after intoxication. The cadmium-induced alterations of the investigated enzymes are discussed in terms of the metabolic disorders produced which are responsible for several pathological conditions.
Heterogeneous inhibition of horseradish peroxidase activity by cadmium
Inhibition of horseradish peroxidase (HRP) activity by cadmium was studied under steady-state kinetic conditions after preincubation of the enzyme with millimolar concentrations of Cd 2 + for various periods of time. The H 2 O 2-mediated oxidation of o-dianisidine by HRP was used to assess the enzymatic activity. Cd 2 + was found to be either a noncompetitive inhibitor of HRP or a mixed inhibitor of HRP depending both on the duration of incubation with HRP and on Cd 2 + concentration. Furthermore, for the same inhibition type, K i values dropped as incubation time increased. These results suggested that Cd 2 + would slowly bind to the enzyme and progressively induce conformational changes. Spectrophotometric analysis showed that indeed Cd 2 + altered the heme Soret absorption band on binding HRP and exhibited a K d which decreased as the incubation time of HRP with Cd 2 + increased. Hill plots suggested a cooperative binding of up to three Cd 2 + ions per molecule of HRP. Thus, Cd 2 + binding to HRP resulted in progressive inhibition of enzymatic activity with a change in the inhibition type as the number of Cd 2 + ions per HRP molecule increased. Results also illustrated the potential danger of long-term exposure to heavy metals, even for enzymes with low affinity for them.
Molecular inhibitory mechanisms of antioxidant enzymes in rat liver and kidney by cadmium
Toxicology, 2002
Catalase, Mn-superoxide dismutase (MnSOD) and Cu,Zn-superoxide dismutase (CuZnSOD) activities were studied in rat liver and kidney 6-48 h after CdCl 2 intraperitoneal administration or 10 -30 days daily oral CdCl 2 intake in drinking water. This approach provided some indications as to the sensitivity of each enzyme to cadmium toxicity. These experiments showed that the formation of thiobarbituric acid reactive substance (TBARS) did not strictly depend on how well the antioxidant enzyme worked. From in vitro experiments it appeared that TBARS removal by vitamin E did not restore the three enzyme activities at all. As for cadmium's inhibitory mechanism on catalase activity, our data, obtained in the pH range 6.0-8.0, are a preliminary indication that the negative effect of this metal is probably due to imidazole residue binding of His-74 which is essential in the decomposition of hydrogen peroxide. Cadmium inhibition of liver mitochondrial MnSOD activity was completely removed by Mn 2 + ions, suggesting that the reducing effect on this enzyme is probably due to the substitution of cadmium for manganese. We also observed the antioxidant capacity of Mn 2 + ions, since they were able to normalize the increased TBARS levels occurring when liver mitochondria were exposed to cadmium. The reduced activity of CuZnSOD does not seem to be due to the replacement of Zn by Cd, nor to the peroxides formed. As this enzyme activity was almost completely recovered after 48 h, we hypothesize that the momentary inhibition is imputable to a cadmium/enzyme interaction. This causes some perturbation in the enzyme topography which is critical for its catalytic activity. The pathological implications linked to antioxidant enzyme disorders induced by cadmium toxicity are discussed.
Cadmium inhibits the electron transfer chain and induces Reactive Oxygen Species
Free Radical Biology and Medicine, 2004
Recent research indicates that cadmium (Cd) induces oxidative damage in cells; however, the mechanism of the oxidative stress induced by this metal is unclear. We investigated the effects of Cd on the individual complexes of the electron transfer chain (ETC) and on the stimulation of reactive oxygen species (ROS) production in mitochondria. The activity of complexes II (succinate:ubiquinone oxidoreductase) and III (ubiquinol:cytochrome c oxidoreductase) of mitochondrial ETC from liver, brain, and heart showed greater inhibition by Cd than the other complexes. Cd stimulated ROS production in the mitochondria of all three tissues mentioned above. The effect of various electron donors (NADH, succinate, and 2,3-dimethoxy-5-methyl-6-decyl-1,4-benzoquinol) on ROS production was tested separately in the presence and in the absence of Cd. ESR showed that complex III might be the only site of ROS production induced by Cd. The results of kinetic studies and electron turnover experiments suggest that Cd may bind between semiubiquinone and cytochrome b 566 of the Q 0 site of cytochrome b of complex III, resulting in accumulation of semiubiquinones at the Q 0 site. The semiubiquinones, being unstable, are prone to transfer one electron to molecular oxygen to form superoxide, providing a possible mechanism for Cd-induced generation of ROS in mitochondria. Published by Elsevier Inc.
Oxidoreductase in rats intoxicated with cadmium
Zbornik Matice srpske za prirodne nauke, 2002
There are a lot of literature data concerning the toxicity of cadmium on liver and kidney. The present work is concerning with the investigation of the effect of two plant extracts: Alloe and Allium sativum and an alcoholic Propolis extract on the behavior of the antioxidant systems. There were studied especially the activity of three enzymes: catalase, methaemoglobine reductase and superoxid dismutase consecutive an installed oxidative stress after cadmium administration in single doze.
Biological Trace Element Research, 2000
Cadmium is known as to be a potent pulmonary carcinogen to human beings and to induce prostate tumor. The sequestration of cadmium, an extremely toxic element to living cells, which is performed by biological ligands such as amino acids, peptides, proteins or enzymes is important to minimize its participation in such deleterious processes. The synthesis of metallothionein is induced by a wide range of metals, in which cadmium is a particularly potent inducer. This protein is usually associated with cadmium exposure in man. Because metallothioneins may act as a detoxification agent for cadmium and chelation involves sulfur donor atoms, we administered only cadmium, cysteine, or methionine to rats and also each of these S-amino acids together with cadmium and measured the production of superoxide radicals derived from the conversion of xanthine dehydrogenase to xanthine oxidase. It could be seen in this work that the presence of cadmium enhances this conversion. However, its inoculation with cysteine or methionine almost completely diminishes this effect and this can be the result of the fact that these amino acids complex Cd(II). Thus, these compounds can be a model of the action of
Effects of cadmium on manganese peroxidase
European journal of biochemistry, 2000
Inhibition of manganese peroxidase by cadmium was studied under steady-state and transient-state kinetic conditions. Cd II is a reversible competitive inhibitor of Mn II in the steady state with K i < 10 mm. Cd II also inhibits enzyme-generated Mn III ±chelate-mediated oxidation of 2,6-dimethoxyphenol with K i < 4 mm. Cd II does not inhibit direct oxidation of phenols such as 2,6-dimethoxyphenol or guaiacol (2-methoxyphenol) in the absence of Mn II. Cd II alters the heme Soret on binding manganese peroxidase and exhibits a K d < 8 mm, similar to Mn (K d < 10 mm). Under transient-state conditions, Cd II inhibits reduction of compound I and compound II by Mn II at pH 4.5. However, Cd II does not inhibit formation of compound I nor does it inhibit reduction of the enzyme intermediates by phenols in the absence of Mn II. Kinetic analysis suggests that Cd II binds at the Mn II-binding site, preventing oxidation of Mn II , but does not impair oxidation of substrates, such as phenols, which do not bind at the Mn II-binding site. Finally, at pH 4.5 and 55 8C, Mn II and Cd II both protect manganese peroxidase from thermal denaturation more efficiently than Ca II , extending the half-life of the enzyme by more than twofold. Furthermore, the combination of half Mn II and half Cd II nearly quadruples the enzyme half-life over either metal alone or either metal in combination with Ca II .