Enantiocomplementary reduction of 3-phenylthiopropan-2-one by Bacillus sp.: effect of medium components.

The enantioselectivity of the enzymes responsible for reduction of prochiral compound 3-phenylthiopropan-2-one was dependent on the concentration of yeast extract and glucose in the growth medium. Low concentrations of yeast extract (0.1-0.9% w/v) favored the formation of S-enantiomer (62% ee at 0.1% w/v yeast extract) of 3-phenylthiopropan-2-ol. However, R-enantiomer of the reduced product was formed when MSM was supplemented with yeast extract at a concentration of 1% (w/v) or more with a maximum ee of 85% at 2.0% (w/v) yeast extract supplement in the growth medium.

Shear bond strength of composite resin to dentin after application of cavity disinfectants - SEM study.

AIM: The aim was to evaluate the effect of different cavity disinfectants on dentin bond strengths of composite resin applied with two different adhesive systems. MATERIALS AND METHODS: Two-hundred mandibular molars were sectioned parallel to the occlusal surface to expose dentin in the midcoronal one-third. The dentinal surfaces were polished with waterproof-polishing papers. The specimens were randomly divided into five groups of 40 teeth each as follows: group 1(control) -- specimens were not treated with any cavity disinfectants. Groups 2--5 (experimental groups) -- dentin surfaces were treated with the following cavity disinfectants, respectively; 2% chlorhexidine solution, 0.1% benzalkonium chloride-based disinfectant, 1% chlorhexidine gel, and an iodine potassium iodide/copper sulfate-based disinfectant. The specimens were then randomly divided into two subgroups including 20 teeth each to evaluate the effect of different bonding systems. Dentin bonding systems were applied to the dentin surfaces and the composite buildups were done. After the specimens were stored in an incubator for 24 hours, the shear bond strength was measured at a crosshead speed of 1 mm/min. The specimens were then statistically analyzed. STATISTICAL ANALYSIS USED: One way analysis of variance and Tukey-HSD tests were used. RESULTS: There was no significant difference between chlorhexidine gel and control groups regardless of the type of the bonding agent used (P>0.05). On the other hand, pretreatment with benzalkonium chloride-based, iodine potassium iodide/copper sulfate-based disinfectants or chlorhexidine solutions had a negative effect on the shear bond strength of self-etching bonding systems. CONCLUSIONS: The findings of this study suggest that when benzalkonium chloride-based, iodine potassium iodide/copper sulfate-based disinfectants or chlorhexidine solutions are used as a cavity disinfectant, an etch-and-rinse bonding system should be preferred.

Laccase production by some Phlebia species.

The present study was carried out to examine the ability of four species of the genus Phlebia, viz. P. floridensis, P. brevispora, P. radiata and P. fascicularia, to produce the ligninolytic enzyme laccase in liquid culture. P. floridensis was the most active species that even surpassed laccase production by Trametes versicolor, and was chosen for further study. Among several carbon sources tested, malt extract turned out to be the best medium for subsequent laccase concentration by ammonium sulfate precipitation. Specific enzyme activity increased 12-fold during this procedure and a K(m) value of 0.33 mM was calculated for the resulting laccase preparation using guaiacol as the substrate. Concentrated laccase from P. floridensis was relatively thermostable and retained 70% and 15% of its activity after 1 h preincubation at 50 degrees C and 60 degrees C, respectively.