A novel enzymatic production system of optically pure β‐hydroxy α‐amino acids was developed. Two enzymes were used for the system: an N‐succinyl L ‐amino acid β‐hydroxylase (SadA) belonging to the iron(II)/α‐ketoglutarate‐dependent dioxygenase superfamily and an N‐succinyl L ‐amino acid desuccinylase (LasA). The genes encoding the two enzymes are part of a gene set responsible for the biosynthesis of peptidyl compounds found in the Burkholderia ambifaria AMMD genome. SadA stereoselectively hydroxylated several N‐succinyl aliphatic L ‐amino acids and produced N‐succinyl β‐hydroxy L ‐amino acids, such as N‐succinyl‐L ‐β‐hydroxyvaline, N‐succinyl‐L ‐threonine, (2S,3R)‐N‐succinyl‐L ‐β‐hydroxyisoleucine, and N‐succinyl‐L ‐threo‐β‐hydroxyleucine. LasA catalyzed the desuccinylation of various N‐succinyl‐L ‐amino acids. Surprisingly, LasA is the first amide bond‐forming enzyme belonging to the amidohydrolase superfamily, and has succinylation activity towards the amino group of L ‐leucine. By combining SadA and LasA in a preparative scale production using N‐succinyl‐L ‐leucine as substrate, 2.3 mmol of L ‐threo‐β‐hydroxyleucine were successfully produced with 93% conversion and over 99% of diastereomeric excess. Consequently, the new production system described in this study has advantages in optical purity and reaction efficiency for application in the mass production of several β‐hydroxy α‐amino acids.
The mechanisms of formation of many aldehydic lipid oxidation products remain unclear, and the involvement of peroxyl radical additions in some cases was recently suggested. Here, the effect of α-tocopherol, a peroxyl radical trap, on the formation of aldehydic phospholipids from a phosphatidylcholine hydroperoxide was studied by electrospray ionization mass spectroscopy (ESI-MS). Based on the observed differential enhancement or suppression of formation of different aldehydes, new pathways are deduced for aldehyde formation via alkoxyl radicals derived from dihydroperoxy derivatives. 相似文献
The reactions of silanes with carbanions generated on the surface of solid bases bring about the nucleophilic substitution at the Si atom to form Si–C bonds. The reaction of alkynes with silanes afforded alkynylsilanes. For example, the reaction of tert-BuCCH or n-BuCCH with Et2SiH2 in the presence of KNH2/Al2O3 gave tert-BuCCSiEt2H and n-BuCCSiEt2H in a 77% and 67% yield, respectively, at 329 K. Toluene also reacted with Et2SiH2 at 329 K to yield benzyldiethylsilane in a 85% yield. The reactions of 1-alkynes with Me3SiCCH in the presence of KNH2/Al2O3 or KF/Al2O3 resulted in a novel type of metathesis reaction between the two alkynes. For example, the reaction of PhCCH with Me3SiCCH afforded PhCCSiMe3 and HCCH in a high yield. These new types of base-catalyzed reactions provide new synthetic routes for Si–C bond formation. 相似文献
Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were distributed mainly in the sn-1,3 positions of seal oil triglyceride and in the sn-2 position of squid oil triglyceride. Seal oil-rich or squid oil-rich fats having constant saturated/monounsaturated/polyunsaturated
fatty acid (PUFA) and n−6/n−3 PUFA ratios were fed to exogenously hypercholesterolemic rats for 160 d. The control fat contained
linoleic acid as the sole PUFA. Before starting the experimental diets, rats were orally treated with high doses of vitamin
D for 4 d to accelerate atherogenesis. The percentage of arachidonic acid in phosphatidylcholine and phosphatidylethanolamine
of liver, platelets, and aorta was lower in the marine oil groups than in the control group, seal oil being more effective
than squid oil. Maximal platelet aggregation induced by collagen was significantly lower both marine oil groups. Platelet
thromboxane (TX) A2 production induced by collagen or thrombin was markedly reduced by feeding seal or squid oils, the reduction being more pronounced
in the seal oil than in the squid oil group. Aortic prostacyclin (PGI2) production was the same among the three groups. The ratio of the productions of aortic PGI2 and platelet TXA2 was significantly higher in the seal oil than in the control group. Although there was no difference in intimal thickness
among the three groups, the aortic cholesterol content was significantly lower in the marine oil groups than in the control
group. These results showed that the main effects in rats of the different intramolecular distributions of EPA and DHA in
dietary fats were on arachidonic acid content in tissue phospholipids and on platelet TXA2 production. 相似文献
Three squirrel monkeys (Saimiri sciureus) learned to reach toward a container that covered food if a cooperative trainer rewarded such reaches by giving the food. A competitive trainer kept any food found, but wrong selections by this trainer were also rewarded. The monkeys initially reached toward the baited container indiscriminately, but gradually and with the aid of color-cued containers, all 3 reliably reached "honestly" and "deceptively" in the presence of the cooperative and competitive trainers, respectively. The monkeys did not appear to take the trainers' knowledge about the location of the food into account, and deception did not occur if food was placed under the normally unbaited container. With additional containers present, monkeys misled the competitive trainer into selecting the unbaited container farthest from the baited one. Although not indicative of mental attribution, the monkeys' behavior suggests awareness of the acquired communicative function of the reaching response. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献