The effect of Zn2+ on glucose 6-phosphate dehydrogenase activity from Bufo arenarum toad ovary and alfalfa plants

Mechanism(s) of action of heavy metals to investigate the regulation of plastidic glucose-6-phosphate dehydrogenase

The regulation of recombinant plastidic glucose-6P dehydrogenase from Populus trichocarpa (PtP2-G6PDH - EC 1.1.1.49) was investigated by exposing wild type and mutagenized isoforms to heavy metals. Nickel and Cadmium caused a marked decrease in PtP2-G6PDH WT activity, suggesting their poisoning effect on plant enzymes; Lead (Pb⁺⁺) was substantially ineffective. Copper (Cu⁺⁺) and Zinc (Zn⁺⁺) exposition resulted in strongest decrease in enzyme activity, thus suggesting a physiological competition with Magnesium, a well-known activator of G6PDH activity. Kinetic analyses confirmed a competitive inhibition by Copper, and a mixed inhibition by (Cd⁺⁺). Mutagenized enzymes were differently affected by HMs: the reduction of disulfide (C¹⁷⁵–C¹⁸³) exposed the NADP⁺ binding sites to metals; C¹⁴⁵ participates to NADP⁺ cofactor binding; C¹⁹⁴ and C²⁴² are proposed to play a role in the regulation of NADP⁺/NADPH binding. Copper (and possibly Zinc) is able to occupy competitively Magnesium (Mg⁺⁺) sites and/or bind to NADP⁺, resulting in a reduced access of NADP⁺ sites on the enzyme. Hence, heavy metals could be used to describe specific roles of cysteine residues present in the primary protein sequence; these results are discussed to define the biochemical mechanism(s) of inhibition of plant plastidic G6PDH.

Validation of oxidative stress responses in two populations of frogs from Western Ukraine

Although amphibians are considered to be good bioindicators of environmental pollution, few data are available concerning their biochemical parameters in natural populations. We investigated seasonal (spring, summer, autumn) and spatial (wetlands in rural and urban areas) fluctuations of oxidative stress biomarkers in the liver of frog Rana ridibunda in Western Ukraine. The Centroid grouping analysis demonstrated that despite the fluctuations of separate indices, frogs from an urban site in summer and autumn are differed widely from those at the same site in spring and frogs from the rural site in all three seasons, joined in common set. In summer, suppression of Mn-superoxide dismutase and catalase activity, as well as increase in oxidized glutathione and lipid peroxidation levels demonstrate a collapse of antioxidant defense system in frogs from an urban site. The integrated oxidative stress index confirms this conclusion.

Different responses of biochemical markers in frogs (Rana ridibunda) from urban and rural wetlands to the effect of carbamate fungicide

Laboratory studies were conducted to determine the effects of carbamate fungicide TATTU (mixture of propamocarb and mancozeb, 0.091 mg L(-1)) on biochemical markers of exposure in Rana ridibunda from clean (reference) and polluted sites. The untreated animals from the polluted site had lower Cu,Zn- and Mn-superoxide dismutase (SOD) and acetylcholinesterase activity, the levels of lipid peroxidation products (TBARS) and protein carbonyls in the liver and vitellogenin-like proteins (Vtg-LP) in the serum, but higher levels of glutathione in the liver in comparison with untreated frogs from the reference site. Catalase activity, superoxide anion and metallothionein levels were the same in both groups. The animals from two sites demonstrate different response on the effect of TATTU during 14 days. In the frogs from polluted site the oxidative damage (the decrease of Mn-SOD activity, lipids and protein oxidative destruction), neurotoxicity (depletion of acetylcholinesterase activity), and endocrine disruption (increase of Vtg-LP level) were revealed. On the other hand, the part of the indices in the animals from the reference site was unchanged after the treatment and the level of metallothionein was elevated demonstrating the satisfactory ability for the adaptation to unfavourable conditions.

Atrazine concentrations, gonadal gross morphology and histology in ranid frogs collected in Michigan agricultural areas

The triazine herbicide atrazine has been suggested to be a potential disruptor of normal sexual development in male frogs. The goals of this study were to collect native ranid frogs from sites in agricultural and non-agricultural areas and determine whether hypothesised atrazine effects on the gonads could be observed at the gross morphological and histological levels. Juvenile and adult green frogs (Rana clamitans), bullfrogs (R. catesbeiana) and leopard frogs (R. pipiens) were collected in the summers of 2002 and 2003. Atrazine concentrations were below the limit of quantification at non-agricultural sites, and concentrations did not exceed 2 microg/L at most agricultural sites. One concentration greater than 200 microg atrazine/L was measured once at one site in 2002. Hermaphroditic individuals with both male and female gonad tissue in either one or both gonads, were found at a low incidence at both non-agricultural and agricultural sites, and in both adults and juveniles. Testicular oocytes (TO) were found in male frogs at most of the sites, with the greatest incidence occurring in juvenile leopard frogs. TO incidence was not significantly different between agricultural and non-agricultural sites with the exception of juveniles collected in 2003. Atrazine concentrations were not significantly correlated with the incidence of hermaphroditism, but maximum atrazine concentrations were correlated with TO incidence in juvenile frogs in 2003. However, given the lack of a consistent relationship between atrazine concentrations and TO incidence, it is more likely the TOs observed in this study result from natural processes in development rather than atrazine exposure.