Expression and characterization of a novel halohydrin dehalogenase from Tistrella mobilis KA081020-065 / 生物工程学报

Halohydrin dehalogenase is of great significance for biodegradation of the chlorinated pollutants, and also serves as an important biocatalyst in the synthesis of chiral pharmaceutical intermediates. A putative halohydrin dehalogenase (HheTM) gene from Tistrella mobilis KA081020-065 was cloned and over-expressed in Escherichia coli BL21 (DE3). The recombinant enzyme was purified by Ni-NTA column and characterized. Gel filtration and SDS-PAGE analysis showed that the native form of HheTM was a tetramer. It exhibited the highest activity at 50 degrees C. The nature and pH of the buffer had a great effect on its activity. The enzyme maintained high stability under the alkaline conditions and below 30 degrees C. HheTM catalyzed the transformation of ethyl(S)-4-chloro-3-hydroxybutyrate in the presence of cyanide, to give ethyl (R)-4-cyano-3-hydroxybutyrate, a key intermediate for the synthesis of atorvastatin.

Effect of different contrast agent doses on the semi-quantitative parameters of dynamic contrast-enhanced MRI of rodent mammary tumor model / 国际生物医学工程杂志

Objective To explore the effects of different doses of contrast agent (CA) on types of time-signal intensity curves (TICs) and semi-quantitative parameters after dynamic contrast-enhanced MRI (DCE-MRI) on Walker 256 murine breast tumor model.Methods A total of 12 rats burdened Walker256 breast cancer models were established and divided into 3 groups randomly, 4 in each group.Routine MR and DCE-MRI scans of the rats using Bruker Pharmascan 7T MR scanner were performed.Doses for the 3 groups were 0.2, 0.3, and 0.5 mmol/kg, respectively.MR data, TICs types and semi-quantitative parameters from each different dose group were statistically studied and compared to observe the differences.Results Tumors were enhanced significantly after injection.The types of TICs in all tumors were the Ⅲ pattern which was not influenced by CA doses.Semi-quantitative parameters of first enhancement (Efirst), maximal enhancement (Emax), washout enhancement (Ewash), and signal enhancement ratio (SER) showed statistical differences among the three dose groups (P＜0.05).Semi-quantitative parameters of time to peak (Tpeak) and washout velocity (Vwash) showed no statistical differences among the three dose groups (P＞0.05).Mean signal intensity of each group was highly negatively linear correlated with scan times after the peak (r=-0.972, P=0.000;r=-0.971, P=0.000;r=-0.989, P=0.000).The washout slope (slopewash) showed no statistical differences among the three groups (P＞0.05).Conclusions Injection doses of CA didn't change the TIC type, Tpeak, Vwash, and Slopewash.These parameters are comparable among different medical centers and can be considered as prior parameters to monitor the efficacy of neoadjuvant chemotherapy.