Biosynthetic L-tert-leucine using Escherichia coli co-expressing a novel NADH-dependent leucine dehydrogenase and a formate dehydrogenase

BACKGROUND: L-tert-Leucine has been widely used in pharmaceutical, chemical, and other industries as a vital chiral intermediate. Compared with chemical methods, enzymatic methods to produce L-tert-leucine have unparalleled advantages. Previously, we found a novel leucine dehydrogenase from the halophilic thermophile Laceyella sacchari (LsLeuDH) that showed good thermostability and great potential for the synthesis of L-tertleucine in the preliminary study. Hence, we manage to use the LsLeuDH coupling with a formate dehydrogenase from Candida boidinii (CbFDH) in the biosynthesis of L-tert-leucine through reductive amination in the present study. RESULT: The double-plasmid recombinant strain exhibited higher conversion than the single-plasmid recombinant strain when resting cells cultivated in shake flask for 22 h were used. Under the optimized conditions, the double-plasmid recombinant E. coli BL21 (pETDute-FDH-LDH, pACYCDute-FDH) transformed 1 mol·L-1 trimethylpyruvate (TMP) completely into L-tert-leucine with greater than 99.9% ee within 8 h. CONCLUSIONS: The LsLeuDH showed great ability to biosynthesize L-tert-leucine. In addition, it provided a new option for the biosynthesis of L-tert-leucine.

Study on the preparation of ligand of hepatic asialoglycoprotein receptor / 国际生物医学工程杂志

Objective To optimize the preparation of high-efficiency galactocylated poly-L-lysine (Gal-PLL) ligand of the asialoglycoprotein receptor in liver, providing premise and foundation for upper preparation of ultrasound contrast agent of liver targeted nanoscale perfluorocarbon microballoon and the liver targeted molecular imaging. Methods Chemical reactions of reductive amination were carried out on group A and group B according to different proportions of reaction component. Each group was subdivided into three subgroups. In group A, three different molar ratios of D-galactose and poly-L-lysine (PLL) were compounded respectively with equivalent and sufficient reductant borohydride. In group B, identical molar ratios of D-galactose and PLL were compounded respectively with three unequal reductants borohydride. Products of each group were separated and purified by sephadex column to acquire different molecular weight distributions and the results were analyzed. Results In the condition of identical reductant, the peak curve of compound's molecular weight appeared earlier when D-galactose decreased properly. In the condition of identical molar ratio of D-galactose and PLL,the peak curve of compound's molecular weight appeared also earlier when reductant decreased properly. When the molar ratio of D-galactose and reductant was 1∶1, the peak curve of compound Gal-PLL and free components was more obvious, and the quantity of compound Gal-PLL increased to maximum. Conclusions In the condition of identical reductant, coupling effect of D-galactose and PLL increased when D-galactose decreased properly. In the condition of identical molar ratio of D-galactose and PLL, coupling effect was better when reductant decreased properly. When the molar ratio of D-galactose and reductant was 1∶1, coupling effect of them was the best. The coupling of D-galactose and PLL was related to not only the proportion of D-galactose and PLL, but also the proportion of D-galactose and reductant.

Research on PEGylated uricase by periodate oxidation and reductive- amination / 中国药科大学学报

@#PEGylated uricase was prepared with the N-terminal amino site-specific modification by periodate oxidation followed by reductive-amination. A monomethoxy poly(ethylene glycol)intermediate was synthesized by amidation from monomethoxy poly(ethylene glycol)amine hydrochloride 20000(mPEG20000-NH2 ·HCl)with the relative molecular mass of 20 kD and N-(tert-butoxycarbonyl)-L-serine(Boc-Ser-OH), and then the Boc group of the intermediate was removed by trifluoroacetic acid(TFA)to produce the desired product Ser-mPEG20000. This compound could be oxidated by periodate to obtain a new poly(ethylene glycol)aldehyde derivative with high activity, which could be used to modify proteins with the N-terminal amino site-specific PEGylation after ultrafiltration, and the modification conditions to uricase by Ser-mPEG20000 were optimized. The structures of poly(ethylene glycol)intermediate and the target product were characterized by IR and 1H NMR, and the overall yield of the target product was 72. 8%. The preliminary modification to uricase indicated that the desired product Ser-mPEG20000 could modify proteins easily and efficiently. The optimal modification conditions of uricase PEGylated by Ser-mPEG20000 were obtained as follows: the molar ratio of Ser-mPEG20000 to uricase was 2 ∶1; the pH value of solution was 5. 0; the reaction temperature was 25 °C and the reaction time was 6 h.