Nagihan Saglam Ertunga

Partial Purification and Characterization of Armillaria mellea β-Glucosidase

A β-glucosidase from Armillaria mellea, an edible mushroom collected from Hıdırnebi High Plateau (Trabzon, Turkey), was partially purified 41.1-fold by using ion-exchange chromatography and it was biochemically characterized. The enzyme exhibited maximum activity at pH 4.0 and 50°C when p-nitrophenyl-β-D-glucopyranoside was used as a substrate. Km and Vmax values were calculated as 0.3 mM and 3.6 U/mg protein, respectively. A. mellea β-glucosidase was quite stable in the range of pH 3.0–6.0 and 8.0 after 24 h of incubation at 4°C. It was determined that the enzyme was extremely stable in the range of 20–50°C after 1 h incubation. It was also determined that some metal ions and chemicals affected the enzyme activity in different ratios.

Dephytinization of food stuffs by phytase of Geobacillus sp. TF16 immobilized in chitosan and calcium-alginate

ABSTRACT In this work, Geobacillus sp. TF16 phytase was separately immobilized in chitosan and Ca-alginate with the efficiency of 38% and 42%, respectively. These enzymes exhibited broad substrate specificity. Maximal relative phytase activity was measured at pH 5.0 and 95°C and pH 3.0 and 75°C for chitosan and Ca-alginate, respectively. The enzymes were highly stable in a wide pH and temperature range. Values of Km and Vmax were determined as 2.38 mM and 3401.36 U/mg protein for chitosan, and 7.5 mM and 5011.12 U/mg protein for Ca-alginate. The immobilized enzymes showed higher resistance to proteolysis. After 4 h incubation, hydrolysis capacities of chitosan- and Ca-alginate immobilized enzymes for soymilk phytate were calculated as 24% and 33%, respectively. The chitosan- and Ca-alginate immobilized phytases conserved its original activity after 8 and 6 cycles of reuse, respectively. The features of the enzymes were very attractive and they might be useful for some industrial applications.

Purification and Characterization of a Novel Thermostable Phytase from the Thermophilic Geobacillus sp. TF16

ABSTRACT A novel phytase from thermophilic Geobacillus sp. TF16 was purified approximately 5-fold using ammonium sulfate precipitation and ion exchange chromatography, and determined as a single band 106.04 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Optimum temperature and optimum pH were found to be 85°C and 4.0, respectively. The enzyme is highly thermostable and Vmax and Km values were calculated as 526.28 U/mg and 1.31 mM, respectively. It was also found that the enzyme exhibited a broad substrate selectivity and resistance toward proteases and effectively hydrolyzed soymilk phytate. These results suggest that this study provides an alternative phytase enzyme with enhanced properties.

Investigation of DNA cleavage activities of new oxime-type ligand complexes and molecular modeling of complex-DNA interactions

Nucleolytic activities of some new oxime-type ligand complexes were investigated by neutral agarose gel electrophoresis. Analysis of the cleavage products in agarose gel indicated that all complexes used converted supercoiled pUC18 plasmid DNA to its nicked or linear form. It was found that nucleolytic activities of the complexes depend on the complex concentration, reaction time and the presence of a cooxidant (magnesium monoperoxyphthalate, MMPP) in the reaction mixture. However, the complexes cleaved pUC18 plasmid DNA at all investigated pH values. Nucleolytic activities of complexes were investigated for different complex concentrations (0.1–100 μmol L−1), pH values (6.0–10.0) and reaction times (0–60 min). Molecular modeling studies performed by the Hyperchem Software together with DNA-binding studies showed that planar sites of the complexes intercalated into double stranded DNA. It can be concluded that all oxime-type ligand complexes used can be evaluated as nuclease mimics.