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The distribution of glucagon-like peptide 1 (GLP-1)-positive cells in digestive tracts and pancreases of aquatic vertebrates was investigated by immunohistochemical staining method. The results suggested that GLP-1-positive cells were distributed in the columnar mucous epithelium and tubular glands of lamina propria in the digestive system. However, GLP-1-positive cells were also found in subepithelial lamina propria of the mucosae and muscularis in each segment of the digestive tract of Rana nigromaculata. The distribution densities of these cells reached peaks in the stomachs, and the middle or end segments of small intestines of Chinese softshell turtle, Bufo gargarizans, R. nigromaculata and catfish, and there was the third distribution density peak in the rectum of catfish. The total amount or overall density of GLP-1-positive cells varied a lot in the digestive tracts of different animal species. The distribution density was relatively low in the digestive tract of chub and reached the maximum in the digestive tracts of snakehead and catfish, but no GLP-1-positive cells were found in the digestive tract of bighead carp. GLP-1-positive cells were densely distributed in the pancreases of Chinese softshell turtle, B. gargarizans and R. nigromaculata. These cells spread over the superficial layers of islets or scattered in exocrine pancreas in the pancreas of B. gargarizans, spread in the endocrine cells or scattered in the pancreas of Chinese softshell turtle, scattered in the pancreas of R. nigromaculata and distributed in the superficial layers of islets in the pancreas of catfish.

A key step during the biosynthesis of cytochalasans is a proposed Knoevenagel condensation to form the pyrrolone core, enabling the subsequent 4+2 cycloaddition reaction that results in the characteristic octahydroisoindolone motif of all cytochalasans. In this work, we investigate the role of the highly conserved a,ß-hydrolase enzymes PyiE and ORFZ during the biosynthesis of pyrichalasin H and the ACE1 metabolite, respectively, using gene knockout and complementation techniques. Using synthetic aldehyde models we demonstrate that the Knoevenagel condensation proceeds spontaneously but results in the 1,3-dihydro-2H-pyrrol-2-one tautomer, rather than the required 1,5-dihydro-2H-pyrrol-2-one tautomer. Taken together our results suggest that the a,ß-hydrolase enzymes are essential for first ring cyclisation, but the precise nature of the intermediates remains to be determined. © 2020 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH

On November 10, 2016, the pulsar navigation test satellite 01 (XPNAV-01) was launched in Jiuquan Satellite Launch Center, and has currently obtained a lot of observation data. At present, the payload has obtained a huge amount of observation data, and the flux, spectrum, and profile of the target observed are obtained as well. High consistency with the observation data by other missions such as RXTE is shown. The function and performance of China’s first grazing incidence X-ray optics onboard XPNAV-01 was verified in-orbit.

Cytochalasans are one type of PKS-NRPS secondary metabolites. The tailoring steps involved in cytochalasan biosynthesis are almost clear, but the formation of the isoindolone core is still mysterious. The ACE1 metabolite probably belongs to the cytochalasan family based on the biosynthetic gene cluster (BGC) analysis, even though the structure is not yet elucidated. Heterologous expression of ace1 (PKS-NRPS) and rap1 (trans-ER) in A. oryzae produced an unexpected alcohol, which is unlikely to undergo further Knoevenagel reaction. Therefore it is deduced to be a shunt metabolite during heterologous expression. To investigate the biosynthesis of the cytochalasan skeleton including reductive release, putative Knoevenagel condensation and Diels-Alder reaction, three model compounds mimicking the ACE1 metabolite precursor were designed, prepared and applied for in vitro assays. Model A was designed and synthesized for over-reduction investigation. In vitro assays confirmed that model A can be reduced to the corresponding primary alcohol by A. oryzae cell free extract. This indicates that the alcohol is a shunt metabolite and A. oryzae is not a suitable host for cytochalasan heterologous expression. Model B was designed and prepared to study Knoevenagel condensation. In vitro assays with model B suggested model B can possibly form pyrrolinone spontaneously in buffer, while pyrrolinone was converted rapidly to alcohols. However, no enzyme activity was observed. Besides, pyrrolinone tautomerism was further investigated by comparing tautomerized pyrrolinone and non-tautomerised pyrrolinone. From NMR and UV analysis, it is confirmed that pyrrolinones tautomerises and are no longer competitive for the following Diels-Alder reaction. Model C was designed for both Knoevenagel condensation and Diels-Alder reaction tests. In vitro Assays showed that pyrrolinone was formed spontaneously, further confirming the Knoevenagel condensation is spontaneous. But its corresponding pyrrolinone also tautomerised and is no longer suitable for the following Diels-Alder reaction.