The gene encoding thermostable lactate dehydrogenase (Tm-LDH) was cloned into the plasmid pHsh from Thermotoga maritima, and expressed in Escherichia coli JM 109. The recombinant protein was purified to homogeneity by a simple step, heat treatment. The recombinant enzyme had a molecular mass of 33 kDa. The optimal temperature and pH of Tm-LDH were observed 95 degrees C and 7.0. The purified enzyme had a half-life of 2 h at 90 degrees C, and exhibited better stability over a pH range from 5.5 to 8.0. The K(m) and V(max) values were 1.7 mmol/L, 3.8 x 10(4) U/mg of protein for pyruvate, and 7.2 mmol/L and 1.1 x 10(5) U/mg for NADH, respectively. The expression of Tm-LDH in T7 system could not obtain high efficiency, but it has been soluble over-expression in pHsh system and reached 340 mg/L. The superior stability and productivity of Tm-LDH will lay the foundation of its industrial-scale fermentation and application in the NAD regeneration.
Cloning, Molecular ; Enzyme Stability ; Escherichia coli ; metabolism ; L-Lactate Dehydrogenase ; biosynthesis ; Molecular Weight ; Recombinant Proteins ; biosynthesis ; Temperature ; Thermotoga maritima ; enzymology

AIM:To investigate the role of anti-miR-21 oligonucleotide ( AMO) in the anti-leukemic activity of decitabine (DCA) in vitro.METHODS:AMO and scramble oligonucleotide (SCR) were constructed and transfected into HL-60 cells.The miR-21 expression was analyzed by real-time PCR to identify the transfection efficiency .The cells were treated with DCA at gradient concentrations (0.5, 2.0 and 4.0 μmol/L) for 48 h.The mRNA expression of human period circadian protein 3 (hPer3) was detected by real-time PCR.The early apoptotic rates were determined by flow cy-tometry with Annexin V/PI staining.Mean fluorescence intensities ( MFI) of CD117 and CD11b were also measured by flow cytometry.RESULTS:The miR-21 relative expression level in AMO group was significantly lower than that in blank group and SCR group (P<0.01).IC50 of DCA in AMO group was significantly lower than that in blank group and SCR group (P<0.01).With the same concentration of DCA, the early apoptotic rate, the mRNA expression of hPer3 and the MFI of CD11b in AMO group were significantly higher than those in blank group and SCR group (P<0.01).The MFI of CD117 in AMO group were significantly lower than those in blank group and SCR group ( P<0.01 ) .CONCLUSION:Activation of hPer3 expression plays an important role in enhanced anti-leukemic activity of decitabine by AMO in vitro.