This study investigated seasonal variations of antioxidant defense enzyme activities: total, manganese, copper zinc containing superoxide dismutase (Tot SOD, Mn SOD, CuZn SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione reductase (GR) and biotransformation phase II enzyme glutathione-S-transferase (GST) activity in the liver and white muscle of red mullet (L. this study was to explore seasonal variations in the activity of the antioxidant defense enzymes: total superoxide dismutase (Tot SOD), manganese comprising superoxide dismutase (Mn SOD), copper zinc comprising superoxide dismutase (CuZn SOD), (EC 220.127.116.11), catalase (CAT, EC 18.104.22.168), glutathione peroxidase (GSH-Px, EC 22.214.171.124), glutathione reductase SMI-4a (GR, EC 126.96.36.199), and the activity of biotransformation phase II enzyme glutathione-S-transferase (GST, EC 188.8.131.52) in the liver and white muscle mass of red mullet (at both sites in winter season and spring is shown in Table 2. The offered results display that total protein concentration was significantly higher in the liver than in white muscle mass at both sites and months. Total protein concentration was significantly reduced the fish liver from Estuary of the River Bojana in spring in respect to winter season (p < 0.05). In contrast, total protein concentration was markedly higher in the white muscle mass from near Pub in spring in comparison to winter season (p < 0.05). These data suggest different metabolic activity of these two tissues in respect to time of year and probably depend on food availability and feeding behavior. Table 2 Total protein concentration (mg/g damp mass) in the liver and white muscle mass of red mullet (L.) from your Near Pub (NB) and Estuary of the River Bojana (EB) in winter season and spring. The data are indicated as mean S.E. The non-parametric ... The obtained results of the activity of antioxidant defense enzymes and biotransformation phase II enzyme GST support the hypothesis of seasonal patterns of antioxidant defense enzymes in the liver and white muscle mass of reddish mullet. Our results display that Mn SOD activity was significantly lower in spring in comparison to winter season (p < 0.05) in the liver (Figure 2A) at both examined localities, and in white muscle (Figure 2B) in NB locality. In addition, Mn SOD activity was significantly lower in spring compared to winter season at EB than at NB (p < 0.05) in both the liver and the white muscle (Figure 2A and 2B). Number SMI-4a 2 The activity (U/mg protein) SMI-4a of Tot SOD, CuZn SOD and Mn SOD in the liver (A) and white muscle mass (B) of reddish mullet (a designated reduction in the antioxidative defense system occurred during winter season . This may be associated with changes in environmental temp, as well as with gonad maturation and food availability. Many other enzymes have reduced activities at lower environmental temp: xanthine dehydrogenase activity in mussels from your Atlantic Ocean , GST activity in viviparous blenny, in the Baltic Sea . However, some enzymes increase their activities in winter season, e.g., etoxycoumarin and etoxyresorufin O-dealkylases in reddish mullet, . Sheehan and Power  conclude that the use of bioindicators, such as enzyme activities, in biomonitoring studies is definitely often complicated, because levels of chemical pollutants in the environment often display wide seasonal variations in response to weather and additional factors. Where such molecules show seasonal variance, this should become incorporated into the interpretation of biomonitoring studies by the use of appropriate controls. Our earlier investigations at the same localities  showed no significant variations in concentrations of polychlorinated biphenyls (PCBs) in both months. It is hard to forecast the direct influence of toxic compounds on antioxidant defense enzyme activities, because the scenario is complicated with seasonal influences. It is well known that in aquatic ecosystems, temp and dissolved oxygen are environmental variables that are likely to influence oxidative processes, even more than xenobiotics. The overall tendency obtained in our study, revealed decreased activities of the investigated enzymes in spring when compared to winter season. Proteins constitute a target for oxidative damage with subsequent alteration of their functions. Studies by additional authors reported that flounders, living in contaminated waters with xenobiotics, showed increased levels of oxidized proteins . The major difference in our work Rabbit Polyclonal to RFWD2 (phospho-Ser387) was found for Mn SOD activity in the liver and white muscle mass of reddish mullet, suggesting that in mullets, the liver mitochondria could efficiently deal with the increase in superoxide anion radicals . It has to be referred that the food uptake can have an effect on antioxidant defense enzyme activities and oxidative stress, as the fish do not eat during the depuration period, as Pascual L.) were caught by trawling in winter season (February) and late spring (May) at two localities: Near Pub (NB) and Estuary of the River Bojana (EB) in the Southern Adriatic Sea. The two localities were chosen in order to compare the activity of antioxidant defense enzyme activities between periods of low metabolic activity in winter season and basal metabolic activity in spring..