L-arabinose isomerase (L-AI) is the key enzyme that isomerizes D-galactose to D-tagatose. In this study, to improve the activity of L-arabinose isomerase on D-galactose and its conversion rate in biotransformation, an L-arabinose isomerase from Lactobacillus fermentum CGMCC2921 was recombinantly expressed and applied in biotransformation. Moreover, its substrate binding pocket was rationally designed to improve the affinity and catalytic activity on D-galactose. We show that the conversion of D-galactose by variant F279I was increased 1.4 times that of the wild-type enzyme. The K_m and k_cat values of the double mutant M185A/F279I obtained by superimposed mutation were 530.8 mmol/L and 19.9 s^-1, respectively, and the catalytic efficiency was increased 8.2 times that of the wild type. When 400 g/L lactose was used as the substrate, the conversion rate of M185A/F279I reached a high level of 22.8%, which shows great application potential for the enzymatic production of tagatose from lactose.
Galactose/metabolism* ; Limosilactobacillus fermentum/genetics* ; Lactose ; Hexoses/metabolism* ; Aldose-Ketose Isomerases/genetics* ; Hydrogen-Ion Concentration

OBJECTIVETo observe the effect of different nutritional routes of giving nutrition on the intestinal mucus barrier in severely scalded rats.

METHODSWistar rats inflicted with 30% TBSA III degree scalding on the back were employed as the model and were randomly divided into 3 groups, i.e. control (C), parenteral nutrition (PN) and enteral nutrition (EN) groups. The rats in PN and EN groups were supplied with equal amount of nitrogen and calories and with equal volume of nutrition solution. The dynamic changes in the thickness of intestinal mucus layer and the contents of protein, hexose and acetylneuraminate in the mucus were examined.

RESULTSWhen compared with those in C group, the intestinal mucus layer became thinner and the contents of protein, hexose and acetylneuraminate in the mucus in both PN and EN groups decreased evidently after scalding. When compared between two nutritional groups, the thickness of intestinal mucus layer and the contents of the hexose and acetylneuraminate in the mucus in EN were much thicker and higher than those in PN group, while the mucus protein content exhibited no obvious difference between PN and EN groups.

CONCLUSIONIt was suggested that intestinal goblet cell synthesized and secreted less mucus after scalding in rats resulting in thinning of intestinal mucus layer and the change in mucus components. When compared with those in PN group, less injury to the intestinal goblet cells occurred and the intestinal mucus synthesis was less affected in EN group, and the components of intestinal mucus were maintained stable.

Animals ; Burns ; metabolism ; Enteral Nutrition ; Female ; Hexoses ; metabolism ; Intestinal Mucosa ; metabolism ; pathology ; Male ; Parenteral Nutrition ; Proteins ; metabolism ; Rats ; Rats, Wistar ; Sialic Acids ; metabolism ; Time Factors

L-Arabinose isomerase (L-AI) is an intracellular enzyme that catalyzes the reversible isomerization of D-galactose and D-tagatose. Given the widespread use of D-tagatose in the food industry, food-grade microorganisms and the derivation of L-AI for the production of D-tagatose is gaining increased attention. In the current study, food-grade strains from different foods that can convert D-galactose to D-tagatose were screened. According to physiological, biochemical, and 16S rDNA gene analyses, the selected strain was found to share 99% identity with Pediococcus pentosaceus, and was named as Pediococcus pentosaceus PC-5. The araA gene encoding L-AI from Pediococcus pentosaceus PC-5 was cloned and overexpressed in E. coli BL21. The yield of D-tagatose using D-galactose as the substrate catalyzed by the crude enzyme in the presence of Mn2+ was found to be 33% at 40 degrees C.
Aldose-Ketose Isomerases ; biosynthesis ; genetics ; Biotransformation ; Cloning, Molecular ; Escherichia coli ; genetics ; metabolism ; Galactose ; metabolism ; Genetic Vectors ; genetics ; Hexoses ; metabolism ; Pediococcus ; classification ; genetics ; isolation & purification ; Recombinant Proteins ; biosynthesis ; genetics

A novel reaction-enzymatic ammonolysis discovered in the mid of 1990s has been demonstrated to be a very promising alternative in the preparation of optically pure compounds. The effects of organic solvent, initial water activity, temperature and additives on lipase Novozym435-catalyzed enantioselective ammonolysis of racemic phenylglycine methyl ester were investigated systematically in this paper. Enzymatic reaction of ammonolysis showed higher activity and enantioselectivity than the corresponding reaction of hydrolysis and alcoholysis.
Alcohols ; Ammonia ; Catalysis ; Dimethylformamide ; pharmacology ; Esters ; Glycine ; analogs & derivatives ; metabolism ; Hexoses ; pharmacology ; Hydrolysis ; Lipase ; drug effects ; metabolism ; Organic Chemicals ; Solvents ; Surface-Active Agents ; pharmacology ; Temperature ; Water

D-psicose 3-epimerase (DPEase) is demonstrated to be useful in the bioproduction of D-psicose, a rare hexose sugar, from D-fructose, found plenty in nature. Clostridium cellulolyticum H10 has recently been identified as a DPEase that can epimerize D-fructose to yield D-psicose with a much higher conversion rate when compared with the conventionally used DTEase. In this study, the crystal structure of the C. cellulolyticum DPEase was determined. The enzyme assembles into a tetramer and each subunit shows a (β/α)(8) TIM barrel fold with a Mn(2+) metal ion in the active site. Additional crystal structures of the enzyme in complex with substrates/products (D-psicose, D-fructose, D-tagatose and D-sorbose) were also determined. From the complex structures of C. cellulolyticum DPEase with D-psicose and D-fructose, the enzyme has much more interactions with D-psicose than D-fructose by forming more hydrogen bonds between the substrate and the active site residues. Accordingly, based on these ketohexose-bound complex structures, a C3-O3 proton-exchange mechanism for the conversion between D-psicose and D-fructose is proposed here. These results provide a clear idea for the deprotonation/protonation roles of E150 and E244 in catalysis.
Binding Sites ; Biocatalysis ; Catalytic Domain ; Clostridium cellulolyticum ; enzymology ; Hexoses ; chemistry ; Manganese ; chemistry ; Protein Structure, Quaternary ; Racemases and Epimerases ; chemistry ; metabolism ; Substrate Specificity

AIMTo study the release and cell uptake characteristics of 9-nitrocamptothecin (9-NC) nanostructured lipid carrier system (NLC) in vitro and its tissue distribution characteristics in vivo.

METHODSMouse peritoneal macrophages were used to investigate the uptake of nanoparticles by cells in vitro. The tissue distribution of 9-nitrocamptothecin solution and stealth nanostructured lipid carrier system (S-NLC) was determined after intravenous administration to mice at a single dose of 1.5 mg kg(-1). The release and crystalloid characteristics were also investigated.

RESULTSX-ray diffraction spectrum showed that 9-NC probably was amorphous in S-NLC. The liquid lipid did not change the characteristics of the solid matrix in nanoparticles. The in vitro release and cell uptake characteristics of stealth and non-stealth 9-NC-NLC were investigated, separately. The results showed that the stealth 9-NC-NLC had sustained-release characteristics and could resist the absorption effect of the additional plasmas to a certain extent. In addition, the cell uptake percentage of stealth 9-NC-NLC was much lower than that of the non-stealth ones. The tissues distribution results showed that 9-NC in the S-NLC was mainly found in the lung, liver, pancreas and ovary/uterus, while the quantity of 9-NC was much lower in heart and kidney. The AUQ(0-t), of S-NLC in blood, ovary/uterus, pancreas, liver and lung were higher than that of 9-nitrocamptothecin solution. The weight-average drug targeting efficiency (Te*) of S-NLC in liver and lung were significantly higher than that of 9-nitrocamptothecin solution. The mean residence times (MRT) of S-NLC was 44 h, while that of 9-nitrocamptothecin solution was 8 h. Therefore, S-NLC showed obvious targeting effects on liver and lung.

CONCLUSIONS-NLC with PEG flexible chains has sustained-release characteristics and can prolong its circulation in blood and have good targeting efficiency on liver and lung.

Animals ; Antineoplastic Agents ; administration & dosage ; chemistry ; pharmacokinetics ; Camptothecin ; administration & dosage ; analogs & derivatives ; chemistry ; pharmacokinetics ; Delayed-Action Preparations ; Drug Carriers ; Drug Delivery Systems ; Female ; Hexoses ; chemistry ; Liver ; metabolism ; Lung ; metabolism ; Macrophages, Peritoneal ; physiology ; Mice ; Nanoparticles ; Particle Size ; Phagocytosis ; Phosphatidylcholines ; chemistry ; Polyethylene Glycols ; chemistry ; Tissue Distribution