Biosynthesis of Streptolidine Involved Two Unexpected IntermediatesProduced by a Dihydroxylase and a Cyclase through UnusualMechanisms

Streptothricin-F (STT-F), one of the early-discovered antibiotics, consists of three components, a β-lysine homopolymer, an aminosugar d-gulosamine, and an unusual bicyclic streptolidine. The biosynthesis of streptolidine is a long-lasting but unresolved puzzle. Herein, a combination of genetic/biochemical/structural approaches was used to unravel this problem. The STT gene cluster was first sequenced from a Streptomyces variant BCRC 12163, wherein two gene products OrfP and OrfR were characterized in vitro to be a dihydroxylase and a cyclase, respectively. Thirteen high-resolution crystal structures for both enzymes in different reaction intermediate states were snapshotted to help elucidate their catalytic mechanisms. OrfP catalyzes an FeII-dependent double hydroxylation reaction converting l-Arg into (3R,4R)-(OH)2-l-Arg via (3S)-OH-l-Arg, while OrfR catalyzes an unusual PLP-dependent elimination/addition reaction cyclizing (3R,4R)-(OH)2-l-Arg to the six-membered (4R)-OH-capreomycidine. The biosynthetic mystery finally comes to light as the latter product was incorporation into STT-F by a feeding experiment

Effect of Cerenkov Radiation-Induced Photodynamic Therapy with 18F-FDG in an Intraperitoneal Xenograft Mouse Model of Ovarian Cancer

Ovarian cancer (OC) metastases frequently occur through peritoneal dissemination, and they contribute to difficulties in treatment. While photodynamic therapy (PDT) has the potential to treat OC, its use is often limited by tissue penetration depth and tumor selectivity. Herein, we combined Cerenkov radiation (CR) emitted by 18F-FDG accumulated in tumors as an internal light source and several photosensitizer (PS) candidates with matched absorption bands, including Verteporfin (VP), Chlorin e6 (Ce6) and 5′-Aminolevulinic acid (5′-ALA), to evaluate the anti-tumor efficacy. The in vitro effect of CR-induced PDT (CR-PDT) was evaluated using a cell viability assay, and the efficiency of PS was assessed by measuring the singlet oxygen production. An intraperitoneal ES2 OC mouse model was used for in vivo evaluation of CR-PDT. Positron emission tomography (PET) imaging and bioluminescence-based imaging were performed to monitor the biologic uptake of 18F-FDG and the therapeutic effect. The in vitro studies demonstrated Ce6 and VP to be more effective PSs for CR-PDT. Moreover, VP was more efficient in the generation of singlet oxygen and continued for a long time when exposed to fluoro-18 (18F). Combining CR emitted by 18F-FDG and VP treatment not only significantly suppressed tumor growth, but also prolonged median survival times compared to either monotherapy

Biosynthesis of Streptolidine Involved Two Unexpected Intermediates Produced by a Dihydroxylase and a Cyclase through Unusual Mechanisms

Streptothricin-F (STT-F), one of the early-discovered antibiotics, consists of three components, a β-lysine homopolymer, an aminosugar D-gulosamine, and an unusual bicyclic streptolidine. The biosynthesis of streptolidine is a long-lasting but unresolved puzzle. Herein, a combination of genetic/biochemical/structural approaches was used to unravel this problem. The STT gene cluster was first sequenced from a Streptomyces variant BCRC 12163, wherein two gene products OrfP and OrfR were characterized in vitro to be a dihydroxylase and a cyclase, respectively. Thirteen high-resolution crystal structures for both enzymes in different reaction intermediate states were snapshotted to help elucidate their catalytic mechanisms. OrfP catalyzes an Fe(II) -dependent double hydroxylation reaction converting L-Arg into (3R,4R)-(OH)2 -L-Arg via (3S)-OH-L-Arg, while OrfR catalyzes an unusual PLP-dependent elimination/addition reaction cyclizing (3R,4R)-(OH)2 -L-Arg to the six-membered (4R)-OH-capreomycidine. The biosynthetic mystery finally comes to light as the latter product was incorporation into STT-F by a feeding experiment

Investigate the Influence of the Quality of the Baking Strength to Camellia Oil

本研究以冷壓法壓榨油茶籽，並由不同烘焙溫度及時間調控茶油製程。溫度因子分為80、100、120、140及160°C五個水準，時間因子分為15、25及35分鐘三個水準。冷壓壓榨方式以兩段式間隔加壓進行，第一階段以加壓時間2.5秒停止12秒的方式，持續加壓至200kg/cm^2，並保持壓力狀態600秒。第二階段加壓方式相同，壓力由200kg/cm^2加壓至550kg/cm^2後，保持壓力狀態2200秒。壓榨所得茶油樣本經沉澱後，逐步進行各項理化特性分析。結果顯示，各試驗組之油樣品過氧化價都低於20毫當量（meq/kg），酸價都在2 mg KOH/g以內。褐變指數與油脂氧化安定性分析結果顯示，安定性最高的試驗組為160°C *35分鐘，所需時間最長可達到5.84 ± 0.17（hrs）。感官品評分析結果顯示，整體喜好度最高試驗組為140°C *15分鐘，其次為120°C *15分鐘。This study use cold pressing process to press camellia oil, and use different roasting temperature and time to control the process. The temperature factor is divided into five levels for 80, 100, 120, 140 and 160 °C. The time factor is divided into three levels for 15, 25, and 35 minutes. The cold pressing method use two-stage approach to provide the pressure intervals. The first stage use 2.5 seconds pressing time and 12 seconds stop time continuing increase the pressure up to 200 kg/cm^2 and maintain this pressure condition for 600 seconds. The second stage use the same pressurized way as the first stage. The pressure increased from 200 kg/cm^2 to 550 kg/cm^2 and maintains the pressure condition for 2200 seconds. After precipitation, the pressed Camellia oil sample had been analyzed for peroxine value, acid value, oil oxidation stability, sensory evaluation and browning index, and try to figure out the best process condition by the integrated analysis

Directly Thiolated Modification onto the Surface of Detonation Nanodiamonds

An efficient method for modifying the surface of detonation nanodiamonds (5 and 100 nm) with thiol groups (−SH) by using an organic chemistry strategy is presented herein. Thiolated nanodiamonds were characterized by spectroscopic techniques, and the atomic percentage of sulfur was analyzed by elemental analysis and X-ray photoelectron spectroscopy. The conjugation between thiolated nanodiamonds and gold nanoparticles was elucidated by transmission electron microscopy and UV–vis spectrometry. Moreover, the material did not show significant cytotoxicity to the human lung carcinoma cell line and may prospectively be applied in bioconjugated technology. The new method that we elucidated may significantly improve the approach to surface modification of detonation nanodiamonds and build up a new platform for the application of nanodiamonds