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关键词： BciC enzyme   Demethoxycarbonylation   Epimerization   Hydrolysis   Hydroxy group   Stereochemistry  

摘要： Zinc methyl pheophorbides a/a', which possess oxo and methoxycarbonyl groups at the C13(1)- and C13(2)-positions, respectively, on the exo- five membered ring fusing the cyclic tetrapyrrole of their chlorin pi-skeletons, were prepared via chemical modifications of chlorophyll a produced in phototrophs. The C13(1)-hydroxylated and unsubstituted analogues were synthesized by reduction of the ketone moiety. The C13(1)- and C13(2)-stereochemistry of these semi-synthetic compounds was confirmed by H-1 NMR and circular dichroism spectroscopies. A methoxycarbonyl group at the chiral C13(2)-position in the ketone was stereo-inverted under basic conditions, whereas those in the corresponding alcoholic and dihydroforms were not. The in vitro BciC enzymatic reaction of the (13(2)R)-ketone was found to stereoselectively hydrolyze the C13(2)-methoxycarbonyl group, followed by spontaneous decarboxylation. Similarly, the (13(2)R)-COOCH3 group in the (13(1)S)-alcohol was hydrolyzed, whereas the (13(2)R)-COOCH3 group in the (13(1)R)-alcohol was not. After the enzymatic reaction of the C13(1)-dihydro-compound, its (13(2)S)-demethoxycarbonylated and hydroxylated product was observed. (C) 2021 Elsevier Ltd. All rights reserved.

关键词： Ti3AlC2   Rice (Oryza sativa L.)   Growth   Stomatal aperture   Trichomes   Antioxidant enzyme  

摘要： MAX phase materials are a new type of nanomaterial with wide applications, but the potential effects of MAX phase materials on plants have not been reported. Herein, we selected Ti3AlC2 nanosheets as a typical MAX phase material to investigate its potential impacts on rice (thyza sativa L) at 0-1000 mu ***(-1). The foliar appli- cation of Ti(3)A(l)C(2) at 100 and 1000 mu ***(-1) inhibited the growth of rice seedlings by producing excess reactive oxygen species (ROS). Furthermore, foliar spraying of Ti3AlC2 at 100 mu g. rnL decreased the stomatal aperture (78.6%) and increased the number of trichomes (100%). These responses demonstrated that the application of Ti3AlC2 could interfere with the immune system of plants by changing the structure and function of leaves. disturbing the activities of antioxidant enzymes. According to the above results, we concluded that the toxicity of Ti3AlC2 nanosheets on plants was mainly caused by the release of titanium ions. This study provides a valuable reference for understanding the impact of MAX phase materials on plants. (C) 2021 Elsevier B.V. All rights reserved.

关键词： Oyster (Crassostrea hongkongensis)   High hydrostatic pressure   Steam treatment   Biochemical composition   Non-volatile taste active compounds  

摘要： In this study, the effects of high hydrostatic pressure (HHP) and steam on biochemical composition and nonvolatile taste active compounds of oysters Crassostrea hongkongensis were investigated. The moisture content in steamed oysters significantly decreased when compared to raw samples, subsequently their crude protein, crude lipid, glycogen and ash contents (% wet weight) were all increased (P < 0.05). In addition, though the moisture content in HHP oysters decreased, no significant differences were observed in proximate compositions compared to raw oysters, except crude protein. There were no significant differences in saturated fatty acids (SFA), monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) profiles between raw and HHP oysters, however, C20:3n6 content in HHP oysters was significantly higher than that in raw samples (P < 0.05). The PUFA profile of steamed oysters, mostly contributed by n-3 PUFA, was significantly higher than that of both raw and HHP samples (P < 0.05). Major free amino acids (FAA) (taste activity value, TAV > 1) in oysters with three treatments were alanine, glycine, glutamic acid and histidine, and their contents were significantly higher in raw and HHP groups than that in steamed group. The 5'-inosine monophosphate (IMP) and 5'-guanosine monophosphate (GMP) in HHP and steamed oysters decreased compared to raw samples, while AMP content in steam oysters were significantly increased (P < 0.05). The equivalent umami concentration (EUC) of oysters of raw, HHP and steamed groups were 8.80, 3.66 and 1.44 g MSG/100 g, respectively, with significant differences observed among different treatments (P < 0.05). Succinic acid was the major organic acid in raw and HHP oysters, while lactic acid was the major organic acid in steamed groups. Further, Na+, K+, PO43- and Cl- were the main inorganic ions (TAV > 1), and their contents were significantly higher in raw and HHP groups than that in steamed group (P < 0.05). This study dem

关键词： Blueberry   PPOs   Purification   Biochemical properties   Binding mechanism  

摘要： Purification of blueberry polyphenol oxidase (PPO) has not been substantially progressed for a long time, which leads to little further study. We purified three PPOs from blueberries for the first time by modified Native-Page. The PPO-2 consists of two subunits (68 and 36 kDa), whereas PPO-3 and PPO-4 contain only one subunit (36 kDa). The optimum pH and temperature of PPO-2, PPO-3, and PPO-4 were 5.8-6.2 and 40 degrees C-45 degrees C with catechol as a substrate. The optimal substrates for them were all catechol (K-m = 14.91, 7.19, and 11.20, respectively). High-pressure processing (HPP) had a limited inhibitory effect on the three PPOs. The activities of PPO-2, PPO-3, and PPO-4 were significantly reduced with increased SDS concentration. The binding of substrate to catalytic cavity is related to the residues His76, His209, His213, Gly228, and Phe230. The carbonyl group of residue Gly228 is one of the key sites for screening substrates.

关键词： Fish health indicators   Salmonids   Farmed fish   Fish blood samples   Reference intervals  

摘要： Blood biochemistry and haematological parameters in fish are affected by environmental changes, nutritional status, stress and health. As such, they are useful indicators of fish health and welfare. However, the correct interpretation of these parameters depends on the availability of species-specific reference values. This study provides baseline data and reference ranges for 34 blood biochemistry and haematological indicators for presumed healthy Chinook salmon, Oncorhynchus tshawytscha, including a comparison of the normal ranges of individuals sampled from freshwater and seawater farms in New Zealand. We found significant differences between the two environments for some parameters, including haematocrit, haemoglobin, sodium, chloride, potassium, globulin, cholesterol, haptoglobin and enzymes including alkaline phosphatase, aspartate aminotransferase and creatinine phosphokinase. We also found that some parameters were significantly correlated with fish size, and in some cases, this relationship was also affected by the environment where the fish was farmed. Our results are an important step forward in developing blood biochemistry and haematology tools to assess the health status of farmed Chinook salmon in New Zealand.