Chemical Synthesis of Phosphorylated Ubiquitin and Diubiquitin Exposes Positional Sensitivities of E1‐E2 Enzymes and Deubiquitinases

Modification of ubiquitin by phosphorylation extends the signaling possibilities of this dynamic signal, as it could affect the activity of ligases and the processing of ubiquitin chains by deubiquitinases. The first chemical synthesis of phosphorylated ubiquitin and of Lys63‐linked diubiquitin at the proximal, distal or both ubiquitins is reported. This enabled the examination of how such a modification alters E1‐E2 activities of the ubiquitination machinery. It is found that E1 charging was not affected, while the assembly of phosphorylated ubiquitin chains was differentially inhibited with E2 enzymes tested. Moreover, this study shows that phosphorylation interferes with the recognition of linkage specific antibodies and the activities of several deubiquitinases. Notably, phosphorylation in the proximal or distal ubiquitin unit has differential effects on specific deubiquitinases. These results support a unique role of phosphorylation in the dynamics of the ubiquitin signal.     

15N tracer application to evaluate nitrogen dynamics of food webs in two subtropical small-scale aquaculture ponds under different managements

Small, semi-intensively managed aquaculture ponds contribute significantly to the food security of small-scale farmers around the world. However, little is known about nutrient flows within natural food webs in such ponds in which fish production depends on the productivity of natural food resources. ¹⁵N was applied as ammonium at 1.1 and 0.4 % of total nitrogen in a traditionally managed flow-through pond and a semi-intensively managed stagnant pond belonging to small-scale farmers in Northern Vietnam and traced through the natural food resources over 7 days. Small-sized plankton (1–60 μ m) was the dominant pelagic biomass in both ponds with higher biomass in the stagnant pond. This plankton assimilated major portions of the applied tracer and showed a high sedimentation and turnover rate. High re-activation of settled nutrients into the pelagic food web was observed. The tracer was removed more quickly from the flow-through pond than from the stagnant pond. A steady nutrient supply could increase fish production.     

Turnover rates in microorganisms by laser ablation electrospray ionization mass spectrometry and pulse-chase analysis

Biochemical processes rely on elaborate networks containing thousands of compounds participating in thousands of reaction. Rapid turnover of diverse metabolites and lipids in an organism is an essential part of homeostasis. It affects energy production and storage, two important processes utilized in bioengineering. Conventional approaches to simultaneously quantify a large number of turnover rates in biological systems are currently not feasible. Here we show that pulse-chase analysis followed by laser ablation electrospray ionization mass spectrometry (LAESI-MS) enable the simultaneous and rapid determination of metabolic turnover rates. The incorporation of ion mobility separation (IMS) allowed an additional dimension of analysis, i.e., the detection and identification of isotopologs based on their collision cross sections. We demonstrated these capabilities by determining metabolite, lipid, and peptide turnover in the photosynthetic green algae, Chlamydomonas reinhardtii, in the presence of ¹⁵N-labeled ammonium chloride as the main nitrogen source. Following the reversal of isotope patterns in the chase phase by LAESI-IMS-MS revealed the turnover rates and half-lives for biochemical species with a wide range of natural concentrations, e.g., chlorophyll metabolites, lipids, and peptides. For example, the half-lives of lyso-DGTS(16:0) and DGTS(18:3/16:0), t_1/2 = 43.6 ± 4.5 h and 47.6 ± 2.2 h, respectively, provided insight into lipid synthesis and degradation in this organism. Within the same experiment, half-lives for chlorophyll a, t_1/2 = 24.1 ± 2.2 h, and a 2.8 kDa peptide, t_1/2 = 10.4 ± 3.6 h, were also determined.     

Effect of Functionalized Magnetite Nanoparticles and Diaminoxanthone on the Curing,Thermal Degradation Kinetic and Corrosion Property of Diglycidyl Ether of Bisphenol A-Based Epoxy Resin

To prepare a high-performance epoxy resin with excellent thermal, chemical and corrosion stability, diaminoxanthone（DAX） was used to cure diglycidylether of bisphenol-A（DGEBA）-based epoxy resin and blend of DGEBA with functionalized Fe3O4 nanoparticles. Kinetic parameters of curing and thermal degradation of epoxy resin systems were estimated by differential scanning calorimetry（DSC） and thermogravimetric analysis（TGA）, respectively. The 10% weight loss temperature has been increased from 340 °C to 366 °C and there was an increase in the char yield from 32.6% to 45.3% for the above systems. The corrosion performance of epoxy coated carbon steel was examined by potentiodynamic polarization, along with immersion test in 1.0 mol/L HCl solution. The results showed that epoxy resins cured with DAX had low tendency to corrosion. In addition, the cured epoxy resin containing 10% Fe3O4 had higher anticorrosion activity than bare DGEBA system. The results showed that functionalized Fe3O4 nanoparticles enhanced char formation and improved the thermal stability as well as anticorrosion activity of the resin.