Thermostability

Bacillus licheniformis WSF-1 strain isolated from sugar distillery plant was capable of producing a maximum amount of EPS (1.24 g/mL) and dry biomass (3.25 g/mL) respectively. Certain factors like inoculum age and carbon source was stand-ardised in view of obtaining high EPS yield. In this study, 48-hold culture was identified as the optimum inoculum age for EPS production. In fermentation, as carbon source plays a major contributing factor that influences the EPS production, optimum carbon source was determined by studying the effect of different carbohydrates such as 12% of glucose, sucrose, lactose, maltose, xylose and fructose on EPS production. The best carbon source was identified as sucrose at a concentration of 25% producing 2.9 g/mL of exopolysaccharide. The polysaccharides were hydrolysed and the monomeric components were determined as fructose and glucose by HPLC, followed by FT-IR analysis. The thermal study revealed that the EPS can withstand high temperature of 219.4 °C and had high glass transition temperature of 150.6 °C. These features indicate the thermo stable nature of the exopolysaccharide which can be used for various industrial applications. Keywords Exopolysaccharide · Bacillus · Thermo stable · Polymer · Carbon source · FTIR · SEM

Amberlite MB-1 was used to immobilize urease (EC.3.5.1.5). The thermal stability of the immobilized urease was better than that of the free urease. Its highest activity was obtained at 75 °C and at pH 6.5 while the optimum temperature for the free urease was found to be 25 °C. Urease immobilized on Amberlite MB-1 retained 65% of the original activity after 5 repeated uses and 62% of the activity after 60 days when stored at 4 °C.

http://link.springer.com/article/10.1007/s004490050397

In this work Azo dye {(2,2 '-(3,3 '-dimethylbiphenyl-4,4 '-diyl) bis (1-(2-hydrazinyl-3,5-dinitrophenyl)diazene)} have been prepared and characterized by, spectorphotometric method UV-Vis, FT-IR spectrum and 1 H-NMR spectrum. The absorption maxima was observed in the 464 nm, Thermogravimetric(TG) and differential scanning calorimetry (DSC) of this compound was measured, The photostability of azo dye in water occurred under UV irradiation processes. Dyeing process has on the dye prepared it gave good results. we have found that the colors of cotton fabrics after dyeing was orange

Urease (EC 3.5.1.5) was covalently attached through glutaraldehyde to partially hydrolysed nylon 6/6 tubes. The highest activity of immobilized enzyme was obtained at 65°C and pH 6.5, while the optimum temperature for free urease was found to be 25°C. Immobilized urease showed an improved thermal stability in comparison to free urease. It retained 76% of the original activity after 60 days when stored at 4°C and 78% of the activity after 5 repeated uses.

http://link.springer.com/article/10.1007/s004490050381

Proteins from hyperthermophilic organisms are typically highly thermostable, and they are optimally active at high temperatures (often 90°C and above). Hyperthermophilic enzymes are surprisingly highly similar to their mesophilic homologs: (i) their sequences are typically 40-85% similar; (ii) their three-dimensional structures are superposable; and (iii) they share the same catalytic mechanisms . Thus, with the exception of phylogenetic variations, what differentiates hyperthermophilic and mesophilic enzymes is only the temperature ranges in which they are stable and active. When cloned and expressed in mesophilic hosts, hyperthermophilic enzymes usually retain their thermal properties, indicating that these properties are genetically encoded. In the few cases where the difference in free energy of stabilization between mesophilic and hyperthermophilic homologous enzymes is known, this difference is small, between 5 and 20 kcal/mol. With the free energy of stabilization provided by non-covalent interactions (i.e., hydrophobic interactions, hydrogen bonds, salt bridges, and aromatic interactions) typically ranging between 0.3 and 2.0 kcal/mol, a small number of additional non-covalent interactions are often enough to explain the remarkable stability of hyperthermophilic enzymes. For this reason, identifying the key stabilizing interactions in a hyperthermophilic protein is a difficult task. This task is made even more difficult by the absence of a single mechanism responsible for protein thermostabilization. Stabilization mechanisms vary from one protein to another. Additional salt bridges and extended salt bridge networks seem to be the most common stabilizing mechanism among different proteins and different organisms (19). Due to the high number of hydrogen bonds in proteins, the role of hydrogen bonds in stabilization has not been extensively studied.

Candida Antarctica Lipase B (CALB) is extensively studied in enzymatic production of biodiesel, pharmaceutical products, detergents and other chemicals. One drawback of using CALB is its relatively low optimum temperature at 313 K (40°C). The objective of this research is to design CALB mutant with improved thermostability by introducing extra disulfide bond. Molecular dynamic simulation was conducted to get better insight into the process of thermal denaturation or unfolding in CALB. Thermal denaturation of CALB was accelerated by conducting simulation at high temperature. Molecular dynamic simulation of CALB was performed with GROMACS software package at 300-700 K. Prediction of possible mutation was done using "Disulfide by Design TM " software. Selection of mutated residues was based on flexibility analysis of CALB. From those analyses, three mutants were designed, which are Mutant-1 (73LeuCys/151AlaCys), Mutant-2 (155TrpCys/294GluCys) and Mutant-3 (43ThrCys/67SerCys). Parameters that were used to compare the thermostability of mutant with wild type enzyme were Root Mean Square Deviations (RMSD), Solvent Accessible Surface Area (SASA), Radius of gyration (Rg) and secondary structure. Molecular dynamic simulation conducted on those three mutants showed that Mutant-1 has better thermostability compared to wild type CALB. We proposed the order of mutant thermostability improvement as follows: Mutant-1, Mutant-2 and Mutant-3, with Mutant-1 having better potential thermostability improvement and Mutant-3, the least stable.

Thermostability of the photosynthetic apparatus of abscisic
acid (ABA)-treated seedlings of barley (Hordeum vulgare) was
studied by light-scattering and by fluorescence measurements of isolated chloroplasts. ABA treatment markedly decreased heat damage of the chloroplast ultrastructure; an exogenous ABA concentration of 10-5 molar was most effective. Heat-induced increase of the 77 chlorophyll fluorescence ratio F740/F685 was also
smaller at this ABA concentration. The heat-induced increase of the initial chlorophyll fluorescence level (Fo) was virtually eliminated
in ABA-treated (10-5 molar) chloroplasts up to 45oC and
slightly increased at 50oC, relative to control chloroplasts where Fo increased even at 35oC and reached its maximal value at 45oC. In control chloroplasts, Fo increased with a 5-minute pretreatment temperature, an effect observed as low as 35oC. Fo was maximal at 45oC. In contrast, chloroplasts treated with 10-5 molar ABA did
not exhibit a heat-induced increase in Fo until 50°C.