Leman Tarhan

The correlation between antioxidant enzyme activities and lipid peroxidation levels in Mentha pulegium organs grown in Ca2+, Mg2+, Cu2+, Zn2+ and Mn2+ stress conditions

The variations of antioxidant enzyme activities and lipid peroxidation (LPO) levels were investigated in all Mentha pulegium organs grown in the excess and absence of Ca2+, Mg2+ as macronutrients; Cu2+, Zn2+ and Mn2+ as micronutrients and control conditions. The decreasing of all antioxidant enzyme activities from roots to leaves, except for ascorbate-dependent peroxidase (AsA-dep POD) and guaiacol-dependent peroxidase (Gua-dep POD) activities under Ca2+ stress conditions caused increases of LPO levels under both Ca2+ and Mg2+ stress conditions. Absence of Ca2+, Mg2+ and Zn2+ caused higher values of superoxide dismutase (SOD) and catalase (CAT) in all organs of M. pulegium than control and maximum increases were obtained in roots as 213.6±4.2 and 45.5±1.3 IU mg−1; 139.9±2.7 and 29.2±0.5 IU mg−1; 140.4±3.0 and 28.0±0.6 IU mg−1 in the absence of Ca2+, Mg2+ and Zn2+, respectively. Whereas the activities increased above control levels under excess Ca2+ and Mg2+ stress conditions, the values were lower than control under excess Zn2+ conditions. Whereas AsA-dep POD activities in Ca2+, Mg2+ and Zn2+ stress conditions were usually lower than control, the lower Gua-dep POD activity values were obtained only in leaves. All these antioxidant enzyme activities correlated positively with increasing Cu2+ concentrations in all M. pulegium organs. SOD and CAT activities under excess Mn2+ conditions were higher, whereas they were lower in the absence of Mn2+ than control. AsA-dep and Gua-dep POD activities were inversely related to SOD and CAT activities. All of stress conditions caused higher LPO levels in all M. pulegium organs than control, except for roots under Ca2+ stress conditions. Whereas absence of Ca2+ and Mg2+ caused maximum LPO levels in leaves, the maximum increases were obtained under excess of Cu2+, Zn2+ and Mn2+ in roots.

Characterization of immobilized catalases and their application in pasteurization of milk with H2O2

The catalase (fromAspergillus niger) has been immobilized by a chemical method on the pous SiO2 modified with γ-aminopropyltrietoxysilane, followed with glutaraldehyde and by a physical method in alginate and γ-carrageenan gel. Optimum support:enzyme ratios and pH values were determined for modified SiO2 in a series of immobilization reactions of catalase in the presence of the crosslinking agent glutaraldehyde, and for alginate and γ-carrageenan in the presence of hemoglobin and bovine serum albimine. pH and temperaturedependent activity variations and the stability properties of immobilized catalase preparations were investigated. Rate constants for H2O2 decomposition and catalase deactivation were determined. The decomposition rate of H2O2 used in the cold pasteurizatioan of milk were investigated in a discontinuous batch type reactor system. Activity half-lives of immobilized catalase were determined.

Effects of antioxidant vitamins A, C, E and trace elements Cu, Se on CuZn SOD, GSH-Px, CAT and LPO levels in chicken erythrocytes.

The biologically damaging effects of reactive oxygen species are controlled in vivo by a wide spectrum of antioxidant defence mechanisms. Dietary constituents of antioxidant vitamins and trace elements may play an important role in protecting against oxidant damage. The effects of supplementation of vitamins A, C, E and trace elements Cu and Se on the activities of antioxidant enzymes and lipid peroxide levels in chicken erythrocytes were investigated depend on the time. CuZnSOD activity and plasma Cu levels in the Cu group were increased by 39 and 37 per cent respectively. CuZnSOD activity in vitamin C groups was also increased by 20 per cent. The GSH‐Px activity in Se, Se+E and Se+Cu groups was raised by 35, 46 and 69 per cent respectively. Also, the GSH‐Px activity in the vitamin C group was increased by 33 per cent. Catalase activity in all of these groups was not significantly different when compared with controls (p<0·01). The maximum decrease in LPO levels of 42 per cent was obtained for the Se+E group. Copyright

Problem‐based learning in an eleventh grade chemistry class: ‘factors affecting cell potential’

The purpose of this research study was to examine the effectiveness of problem‐based learning (PBL) on eleventh grade students’ understanding of ‘The effects of temperature, concentration and pressure on cell potential’ and also their social skills. Stratified randomly selected control and experimental groups with 20 students each were used in this study. To determine their misunderstandings and misconceptions about closely related, previously covered subjects, such as oxidation‐reduction reactions and electrochemical cells, interviews were conducted. Following a preparatory lesson where remediation of misconceptions were undertaken, a pre‐test was given, and no significant difference was found between the two groups of students (p>0.05). Then, the same teacher taught factors that affect cell potential using a teacher‐centred traditional format to the control group, and a PBL format to the experimental group. Results from the post‐test of both groups (p<0.05) showed that PBL is effective on students’ achievement, remedying formation of misconceptions in a significant way. Interviews were also conducted with PBL students to determine their beliefs according to PBL activity. The findings according to interviews revealed that students in the PBL class were more motivated, self‐confident, willing to problem‐solve and share knowledge, and were more active in cooperative group activities than the traditionally‐taught students.

Purification and characterization of superoxide dismutase from chicken liver

Superoxide dismutase (SOD; EC 1.15.1.1) is an enzyme that protects against oxidative stress from superoxide radicals in living cells. This enzyme has been isolated, purified and partially characterized from chicken liver. The following steps were carried out in order to purify chicken liver SOD. Initially, the liver was homogenized and hemoglobin was removed. Subsequently protein precipitation was effected with (NH(4))(2)SO(4), methanol, (NH(4))(2)SO(4)-methanol and polyethylene glycol methods. The product from polyethylene glycol-3350 precipitation was found to have the highest SOD activity. Polyethylene glycol was removed by chromatography using a PD-10 column. After passing through an ultrafilter, the superoxide dismutase was fractionated by DEAE-ion chromatography and then Sephadex G-75 gel filtration chromatography. During this purification procedure, a specific activity of 4818.2 IU/mg was reached, corresponding to 285.8-fold purification. The purified enzyme, which was characterized as cyanide-sensitive SOD, contained two subunits having Cu and Zn elements with a molecular weight of 16000+/-500 for each. The optimum pH of purified CuZnSOD was determined to be 8.9. The enzyme was found to have good pH stability in the pH range 6.0-7.5 at 25 degrees C over a 2-h incubation period and displayed good thermal stability up to 45 degrees C at pH 7.4 over a 1-h incubation period. The SOD enzyme was not inhibited by DTT and beta-mercaptoethanol, but inhibited by CN(-) and H(2)O(2). In the presence of 2 mM iodoacetamide, the enzyme showed an approximately 40% activity loss. Finally, the inhibitory effect of ionic strength on SOD was also investigated.

Use of immobilised catalase to remove H2O2 used in the sterilisation of milk

The sterilisation capacity of H2O2 was determined by investigating the variations of total bacterial and coliform counts with respect to time in raw milk samples containing various amounts of H2O2 at different temperatures. The removal of H2O2 used in milk sterilisation was accomplished by catalase immobilised on DEAE-cellulose, modified initially with 2-amino-4,6-dichloro-s-triazin and then with hexamethylenediamine and glutaraldehyde. To investigate the applicability of immobilised catalase in discontinuous batch and fluidised bed reactor systems, some kinetic parameters were examined and reaction rate constants determined.

Purification and characterization of superoxide dismutase from Phanerochaete chrysosporium

The superoxide dismutase that protects against oxidative stress of superoxide radicals in living cells was isolated and purified from Phanerochaete chrysosporium and partially characterized. Cells cultivated under optimized growth conditions were distrupted by grinding with glass beads in a mixer-mill. Partial protein precipitation in crude extract was affected by using (NH4)2SO4, polyethylene glycol, and methanol methods. Fractionation of superoxide dismutase was performed by O-diethylaminoethyl-cellulose ion-exchange chromatography, followed by Sephadex G-100 gel-filtration chromatography. Purified enzyme has a molecular weight of 44 000 ± 800 and is comprised of two equal sized subunits each having an Mn element. The optimum pH of purified MnSOD was obtained as 8.8. Enzyme remained stable at pH 7.0–8.8, 25°C and up to 45°C at pH 7.4 for 1 h incubation. The enzyme was insensitive to cyanide, hydrogen peroxide, ditiothreitol, sodium azide, Triton X-100, and β-mercaptoethanol and was sensitive to sodium dodecyl sulfate. Phenylmethylsulfonyl fluoride (2 mM) and iodoacetamide showed only a 15% inhibition effect on the enzyme. Up to 50% activity reduction was observed for 100 mM ionic strength of phosphate and chloride.

Active-learning versus teacher-centered instruction for learning acids and bases

Background and purpose Active-learning as a student-centered learning process has begun to take more interest in constructing scientific knowledge. For this reason, this study aimed to investigate the effectiveness of active-learning implementation on high-school students’ understanding of ‘acids and bases’. Sample The sample of this study was 45 high-school students (average age 17 years) from two different classes, which were randomly assigned to the experimental (n = 21) and control groups (n = 25), in a high school in Turkey. Design and methods A pre-test consisting of 25 items was applied to both experimental and control groups before the treatment in order to identify student prerequisite knowledge about their proficiency for learning ‘acids and bases’. A one-way analysis of variance (ANOVA) was conducted to compare the pre-test scores for groups and no significant difference was found between experimental (ME = 40.14) and control groups (MC = 41.92) in terms of mean scores (F 1,43 = 2.66, p > 0.05). The experimental group was taught using an active-learning curriculum developed by the authors and the control group was taught using traditional course content based on teacher-centered instruction. After the implementation, ‘Acids and Bases Achievement Test’ scores were collected for both groups. Results ANOVA results showed that students’ ‘Acids and Bases Achievement Test’ post-test scores differed significantly in terms of groups (F 1,43 = 102.53; p < 0.05). Additionally, in this study 54 misconceptions, 14 of them not reported in the literature before, were observed in the following terms: ‘acid and base theories’; ‘metal and non-metal oxides’; ‘acid and base strengths’; ‘neutralization’; ‘pH and pOH’; ‘hydrolysis’; ‘acid–base equilibrium’; ‘buffers’; ‘indicators’; and ‘titration’. Based on the achievement test and individual interview results, it was found that high-school students in the experimental group had fewer misconceptions and understood the concepts more meaningfully than students in control group. Conclusion The study revealed that active-learning implementation is more effective at improving students’ learning achievement and preventing misconceptions.

Effect of enzyme ratio on the properties of glucose oxidase and catalase immobilized on modified perlite

Processed perlite modified by silanization and treatment with glutaraldehyde was used as a support for the co-immobilization of glucose oxidase and catalase. Immobilization was carried out with several enzyme ratios and activity investigated with respect to pH and temperature. The deactivation rates of the preparations were investigated in recycling fluid bed reactors.

A jigsaw cooperative learning application in elementary science and technology lessons: physical and chemical changes

Background Cooperative learning is an active learning approach in which students work together in small groups to complete an assigned task. Students commonly find the subject of ‘physical and chemical changes’ difficult and abstract, and thus they generally have many misconceptions about it. Purpose This study aimed to investigate the effects of jigsaw cooperative learning activities developed by the researchers on sixth grade students’ understanding of physical and chemical changes. Sample Participants in the study were 61 sixth grade students in a public elementary school in Izmir, Turkey. Design and methods A pre-test and post-test experimental design with a control group was used, and students were randomly assigned to the experimental and control groups. Instruction of the subject was conducted via jigsaw cooperative learning in the experimental group and via teacher-centered instruction in the control group. During the jigsaw process, experimental group students studied the subjects of changes of state, changes in shape and molecular solubility from physical changes, and acid–base reactions, combustion reactions and changes depending on heating from chemical changes in their jigsaw groups. Results The concept test results showed that jigsaw cooperative learning instruction yielded significantly better acquisition of scientific concepts related to physical and chemical changes, compared to traditional learning. Students in the experimental group had a lower proportion of misconceptions than those in the control group, and some misconceptions in the control group were identified for the first time in this study. Conclusions Jigsaw cooperative learning is an effective teaching technique for challenging sixth grade students’ misconceptions in the context of physical and chemical changes, and enhancing their motivation, learning achievements, self-confidence and willingness in the science and technology lesson. This technique could be applied to other chemistry subjects and other grade levels.