Asymmetric reduction of bulky diaryl ketones is still one of the challenging tasks in biocatalysis. By genomic data mining, a putative carbonyl reductase gene pascr was found in Pichia pastoris GS115. pascr was cloned and over-expressed in Escherichia coli Rosseta2 (DE3). The recombinant enzyme was purified to homogeneity by Ni-NTA column and its catalytic properties were studied. PasCR strictly used NADPH as cofactor, gel filtration and SDS-PAGE analysis suggested that the native form of PasCR was a dimmer. PasCR exhibited the highest activity at 35 degrees C in phosphate buffer at pH 6.5. The enzyme catalyzed the reduction of some bulky diaryl ketones, such as 4-methylbenzophenone, 2-methylbenzophenone and 4-chlorobenzophenone, especially for 4-methylbenzophenone, the product S--alcohol was obtained with 85% ee.
Alcohol Oxidoreductases ; genetics ; Amino Acid Sequence ; Catalysis ; Cloning, Molecular ; Ketones ; chemistry ; Molecular Sequence Data ; Pichia ; enzymology ; genetics ; Stereoisomerism

OBJECTIVE：To study the prepar ation technology of gastric floating tablets of Schisandra chinensis total lignans （SCTL），and evaluate the quality of prepared tablets. METHODS ：Based on single factor test ，the orthogonal experiment was conducted to optimize the formulation of SCTL gastric floating tablets with the contents of hydroxypropylmethylcellulose （HPMC） K15M，NaHCO3 and microcrystalline cellulose as the factors ，using starting time ，holding time and cumulative release rate of gastric floating tablets as evaluation indexes. The properties ，weight difference ，floatability and accumulative release rate of the prepared SCTL gastric floating tablets were determined. The gastric floating tablets were qualitatively identified by TLC ，and the contents of schisandrin A and total lignans were determined by HPLC and UV spectrophotometry. RESULTS ：The optimal formulation of SCTL gastric floating tablets was made up of 23％ SCTL extract ，20％ HPMC K 15M，40％ microcrystalline cellulose，15％ sodium bicarbonate ，1％ octadecyl alcohol and 1％ polyvinylpyrrolidone. The results of detection of this preparation were in line with the related provisions of “0101 tablet”stated in 2015 edition of Chinese Pharmacopoeia （part Ⅳ）. TLC indicated that the chromatogram of the test sample showed the main spots of same color as the corresponding positions of the chromatogram of schizandrol A control ，Schisandra chinensis reference substance and raw material ，while the negative control has no interference. Content determination results shows that the average content of schizandrol A and total lignans in SCTL gastric floating tablets is 3.187，19.617 mg. It was preliminarily formulated that the content limitation of schizandrol A in one tablet should not be less than 2.50 mg，and the content of total lignans （calculated by schizandrol A ）should not be less than 15.50 mg. CONCLUSIONS：The preparation technology of SCTL gastric floating tablets is stable ，feasible and controllable in quality.