Metabolic engineering of Escherichia coli for high-level production of violaxanthin.

BACKGROUND: Xanthophylls are a large class of carotenoids that are found in a variety of organisms and play particularly important roles in the light-harvesting and photoprotection processes of plants and algae. Violaxanthin is an important plant-derived xanthophyll with wide potential applications in medicines, foods, and cosmetics because of its antioxidant activity and bright yellow color. To date, however, violaxanthins have not been produced using metabolically engineered microbes on a commercial scale. Metabolic engineering for microbial production of violaxanthin is hindered by inefficient synthesis pathway in the heterologous host. We systematically optimized the carotenoid chassis and improved the functional expression of key enzymes of violaxanthin biosynthesis in Escherichia coli. RESULTS: Co-overexpression of crtY (encoding lycopene ß-cyclase), crtZ (encoding ß-carotene 3-hydroxylase), and ZEP (encoding zeaxanthin epoxidase) had a notable impact on their functions, resulting in the accumulation of intermediate products, specifically lycopene and ß-carotene. A chassis strain that did not accumulate the intermediate was optimized by several approaches. A promoter library was used to optimize the expression of crtY and crtZ. The resulting strain DZ12 produced zeaxanthin without intermediates. The expression of ZEP was further systematically optimized by using DZ12 as the chassis host. By using a low copy number plasmid and a modified dithiol/disulfide system, and by co-expressing a full electron transport chain, we generated a strain producing violaxanthin at about 25.28 ± 3.94 mg/g dry cell weight with decreased byproduct accumulation. CONCLUSION: We developed an efficient metabolically engineered Escherichia coli strain capable of producing a large amount of violaxanthin. This is the first report of a metabolically engineered microbial platform that could be used for the commercial production of violaxanthin.

Safety study on jiazhu vascular ligating clips in rabbits after laparoscopic cholecystectomy / 中国比较医学杂志

Objective To provide an experimental reference for clinic application of Jiazhu vascular ligating clips on ligation effects and the impact on the body in rabbits after laparoscopoic cholecystectomy.Methods 36 rabbits were randomly divided into 3 groups, normal control group, Jiazhu group and similar product control ( Hem-o-lok) group, 12 rabbits in each group.Except for normal control group, the rabbits were used gallbladder duct and gallbladder artery closed by vascular ligating clips and Hem-o-lok clips in Jiazhu group and similar product control group, respectively.The changes of blood biochemical, electrolytes, hematological parameters, coagulation, ligation effects and organ coefficients were observed at post-operation during 12 months.Results Compared with normal control group, the rabbit weight was reduced in the Jiazhu group at 3 days postoperatively ( P 0.05 ) , and there were all no significant differences with electrolyte, coagulation and organ coefficients between each group (P >0.05).Conclusion Jiazhu vascular ligating clips are safe and reliable to close gallbladder duct and blood vessels, It shows that there are no differences in the validity and security between Jiazhu vascular ligating clips and Hem-o-lok clips.

EFFECT OF WHEY PROTEIN PEPTIDES ON ANTIOXIDANT ABILITIES IN AGED MICE / 营养学报

Objective To observe the antioxidant activities of whey protein peptides (WPP) in aged mice.Method The subacute aged model mice were made by neck back subcutaneous injection of D-galactose every day.Compared with VE as positive control,the mice were given three different doses of WPP,100,200,400 mg/(kg bw?d) respectively,the effect of WPP on the content of catalase (CAT),malondialdehyde (MDA),superoxide dismutase (SOD),glutathione peroxidase (GSH-PX)in serum,liver and brain were observed after 45 d.Results The CAT,SOD and GSH-PX activities in aged model group were significantly decreased,but MDA was significantly increased as compared to normal mice.While in the aged mice treated with WPP 200 and 400 mg/(kg bw?d),the activity of CAT,SOD and GSH-PX were significantly increased and the content of MDA significantly decreased as compared to aged mice.Conclusion WPP shows dose-dependant antioxidant effect in aged mice.

DETERMINATION OF FOLIC ACID IN INFANT FORMULA MILK POWDER BY SOLID-PHASE EXTRACTION-REVERSED PHASE HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY / 营养学报

Objective A quick and sensitive method was developed for determination of folic acid (FA) in infant formula milk powder. Method Perchloric aicd was added into infant formula milk powder to extract FA in ultrasonic wave condition. After solid-phase extraction (SPE) with C18 material as plug and reaction with potassium permanganate, FA was determined by reversed phase high-performance liquid chromatography (RP-HPLC). pH 5.0 and 0.1 mol/L sodium dihydrogen phosphate were used as mobile phase. the flow rate was 1 ml/min. BDS C18 was used as separating column and column temperature was 30 ℃. Results The linear range of the method was 0.005-1.5 ?g/ml. The average recovery was 91.7%- 98.3%. The relative standard deviation (RSD) was 2.5%. The limit of detection was 0.005 ?g/ml, and the limit of quantification was 0.017 ?g/ml. Conclusion The method has following advantages: simple, precise, accurate and easy to practice.