1.
Antimicrobial activity of silver loaded MnO2 nanomaterials with different crystal phases against Escherichia coli.
Wang, L, He, H, Zhang, C, Sun, L, Liu, S, Wang, S
Journal of environmental sciences (China). 2016;:112-120
Abstract
Silver-loaded MnO2 nanomaterials (Ag/MnO2), including Ag/α-MnO2, Ag/β-MnO2, Ag/γ-MnO2 and Ag/δ-MnO2 nanorods, were prepared with hydrothermal and impregnation methods. The bactericidal activities of four types of Ag/MnO2 nanomaterials against Escherichia coli were investigated and an inactivation mechanism involving Ag(+) and reactive oxygen species (ROS) was also proposed. The bactericidal activities of Ag/MnO2 depended on the MnO2 crystal phase. Among these nanomaterials, Ag/β-MnO2 showed the highest bactericidal activity. There was a 6-log decrease in E. coli survival number after treatment with Ag/β-MnO2 for 120min. The results of 5,5-dimethyl-1-pyrroline-N-oxide spin-trapping measurements by electron spin resonance indicate OH and O2‾ formation with addition of Ag/β-MnO2, Ag/γ-MnO2 or Ag/δ-MnO2. The strongest peak of OH appeared for Ag/β-MnO2, while no OH or O2‾ signal was found over Ag/α-MnO2. Through analysis of electron spin resonance (ESR) and Ag(+) elution results, it could be deduced that the toxicity of Ag(+) eluted from Ag/MnO2 nanomaterials and ROS played the main roles during the bactericidal process. Silver showed the highest dispersion on the surface of β-MnO2, which promoted ROS formation and the increase of bactericidal activity. Experimental results also indicated that Ag/MnO2 induced the production of intracellular ROS and disruption of the cell wall and cell membrane.
2.
Crystal structures of 2-methylisocitrate lyase in complex with product and with isocitrate inhibitor provide insight into lyase substrate specificity, catalysis and evolution.
Liu, S, Lu, Z, Han, Y, Melamud, E, Dunaway-Mariano, D, Herzberg, O
Biochemistry. 2005;(8):2949-62
Abstract
Two crystal structures of the C123S mutant of 2-methylisocitrate lyase have been determined, one with the bound reaction products, Mg(2+)-pyruvate and succinate, and the second with a bound Mg(2+)-(2R,3S)-isocitrate inhibitor. Comparison with the structure of the wild-type enzyme in the unbound state reveals that the enzyme undergoes a conformational transition that sequesters the ligand from solvent, as previously observed for two other enzyme superfamily members, isocitrate lyase and phosphoenolpyruvate mutase. The binding modes reveal the determinants of substrate specificity and stereoselectivity, and the stringent specificity is verified in solution using various potential substrates. A model of bound 2-methylisocitrate has been developed based on the experimentally determined structures. We propose a catalytic mechanism involving an alpha-carboxy-carbanion intermediate/transition state, which is consistent with previous stereochemical experiments showing inversion of configuration at the C(3) of 2-methylisocitrate. Structure-based sequence analysis and phylogenic tree construction reveal determinants of substrate specificity, highlight nodes of divergence of families, and predict enzyme families with new functions.