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关键词： Electrocatalysts  

摘要： Reduction of oxides and oxoanions of carbon and nitrogen are of great contemporary importance as they are crucial for a sustainable environment. Substantial research has been dedicated to these areas in the last few decades. These reductions require both electrons and protons and their thermodynamic potentials often make them compete with hydrogen evolution reaction i.e., the reaction of protons and electrons to generate H-2. These reactions are abundant in the environment in microorganisms and are facilitated by naturally occurring enzymes. This review brings together the state-of-the-art knowledge in the area of enzymatic reduction of CO2, NO2- and H+ with those of artificial molecular electrocatalysis. A simple ligand field theory-based design principle for electrocatalysts is first described. The electronic structure considerations developed automatically yield the basic geometry required and the 2(nd) sphere interactions which can potentially aid the activation and the further reduction of these small molecules. A systematic review of the enzymatic reaction followed by those reported in artificial molecular electrocatalysts is presented for the reduction of CO2, NO2- and H+. The review is focused on mechanism of action of these metalloenzymes and artificial electrocatalysts and discusses general principles that guide the rates and product selectivity of these reactions. The importance of the 2(nd) sphere interactions in both enzymatic and artificial molecular catalysis is discussed in detail.

关键词： Staphylococcus aureus   RNA polymerase   delta subunit   beta ' jaw   Interaction interface  

摘要： A large class of bacterial RNA polymerase (RNAP) from low-G+C-content Gram-positive bacterial strains, such as the major human pathogen Staphylococcus aureus, not only contain five conserved subunits (a(I), a(II), beta, beta' and u), but also has a delta subunit. Despite being first identified as unique, Grampositive specific component of RNAP apoenzyme more than 30 years ago and reported to be essential for transcription, the structural basis and molecular mechanism of delta subunit in the regulation of transcription remain poorly understood. Here, we performed structural analyses, site-directed mutagenesis and biochemical assays to uncover the interactions of S. aureus d subunit with RNAP core enzyme and DNA towards the understanding of its role in transcription regulation. Microscale thermophoresis (MST) and electrophoretic mobility shift assay (EMSA) of the wild-type and mutated S. aureus d subunit revealed the N-terminal domain of d subunit directly binds to the beta' jaw of S. aureus RNAP (SauRNAP), identified the key amino acid residues (F58, D61, D65, R67 and W81) of d subunit involving in the binding with SauRNAP core enzyme, and uncovered the d subunit C-terminal domain interferes with the interaction between DNA and SauRNAP core enzyme, by which transcription is regulated. Our results provide an excellent starting point for understanding the unique regulatory role and physiological function of d subunit on transcription regulation in Gram-positive bacteria. (C) 2021 Elsevier Inc. All rights reserved.

关键词： Hydrocarbons   High-performance liquid chromatography   Peptides and proteins   Metabolism   Rodent models  

摘要： In mammals, carotenoids are converted by two carotenoid cleavage oxygenases into apocarotenoids, including vitamin A. Although knowledge about beta-carotene oxygenase-1 (BCO1) and vitamin A metabolism has tremendously increased, the function of beta-carotene oxygenase-2 (BCO2) remains less well-defined. We here studied the role of BCO2 in the metabolism of long chain beta-apocarotenoids, which recently emerged as putative regulatory molecules in mammalian biology. We showed that recombinant murine BCO2 converted the alcohol, aldehyde, and carboxylic acid of a beta-apocarotenoid substrate by oxidative deavage at position C9,C10 into a beta-ionone and a diapocarotenoid product. Chain length variation (C20 to C40) and ionone ring site modifications of the apocarotenoid substrate did not impede catalytic activity or alter the regioselectivity of the double bond cleavage by BCO2. Isotope labeling experiments revealed that the double bond cleavage of an apocarotenoid followed a dioxygenase reaction mechanism. Structural modeling and site directed mutagenesis identified amino acid residues in the substrate tunnel of BCO2 that are critical for apocarotenoid binding and catalytic processing. Mice deficient for BCO2 accumulated apocarotenoids in their livers, indicating that the enzyme engages in apocarotenoid metabolism. Together, our study provides novel structural and functional insights into BCO2 catalysis and establishes the enzyme as a key component of apocarotenoid homeostasis in mice.

关键词： Pumpkin   Osborne method   Protein isolate   Essential amino acids nutritional properties   Functional properties  

摘要： Pumpkin seeds are rich source of nutritionally well-balanced proteins. The biochemical, nutritional, and functional properties of the protein isolate (PPI) and protein fractions from pumpkin seed were evaluated. Extraction method for PPI was optimized by varying NaCl (0, 0.5, 1 M) and flour-to-solution ratio (1:5, 1:10, 1:25), at pH 9.0. Proteins were extracted by Osborne procedure and the alkali fraction (AF, 45.82%) was found to be the predominant fraction. SDS-PAGE profile of PPI revealed major bands ranging from 50 to 7 kDa. AF contained all the essential amino acids (EAA) except lysine and threonine, as required by pre-school children (FAO/WHO). PPI and AF showed better protein efficiency ratio and EAA/TAA (total) %, indicating the presence of good quality proteins. Functional properties were found to be comparable with soybean protein isolate. Circular dichroism studies showed that water fraction comprised of alpha-helix and random coils, while salt and alkali fractions contained beta-strand and coils.

关键词： Non-biting midges   Single exposure   Organophosphate   PAHs   Metallic species  

摘要： In-vitro effects of sub-lethal concentrations of malathion, phenanthrene (Phe) and cadmium (Cd) were tested on Chironomus sancticaroli larvae in acute bioassays by measuring biochemical and molecular parameters. Malathion was evaluated at 0.001, 0.0564 and 0.1006 mg L-1;Phe at 0.0025, 1.25 and 2.44 mg L-1;and Cd at 0.001, 3.2 and 7.4 mg L-1. The recovery test carried out at the highest concentration of each compound showed that survival of larvae exposed to Phe ranged from 4% to 5%, while the effects of malathion and Cd were irreversible, not allowing the emergence of adults. Results showed that malathion and Cd inhibited AChE, EST-alpha and ES-beta activities at the two highest concentrations. Phe at 0.0025, 1.25 and 2.44 mg L-1;and Cd at 3.2 and 7.4 mg L-1 inhibited glutathione S-transferase activity. Oxidative stress was exclusively induced by the lowest concentration of malathion considering SOD activity once CAT was unaffected by the stressors. Lipid peroxidation was registered exclusively by malathion at the two highest concentrations, and total hemoglobin content was only reduced by Cd at the two highest concentrations. The relationship among biochemical results, examined using the PCA, evidenced that malathion and Cd concentrations were clustered into two groups, while Phe only formed one group. Four hemoglobin genes of C. sancticaroli were tested for the first time in this species, with Hemoglobin-C being upregulated by malathion. The toxicity ranking was malathion > Phe > Cd, while biochemical and molecular results showed the order malathion > Cd > Phe. Our results highlight the importance of combining different markers to understand the effects of the diverse compounds in aquatic organisms.

关键词： Microalgae biofilm   Chlorella vulgaris   Attached cultivation   Planar waveguide   Light delivery   CO2 bio-fixation  

摘要： Aiming at alleviating the adverse effects on attached microalgae biofilm growth caused by heterogeneous spatial light distributions within the attached cultivation photobioreactors (PBRs), an innovative PBR integrated with stacked horizontal planar waveguide modules (SHPW-PBR) was proposed in this work. Different from the conventional PBR, the emergent light from the external LED light bars were guided and evenly redistributed within the SHPW-PBR by the planar waveguides and hence provided light energy for microalgae cells photoautotrophic growth. In comparison with the control PBR, the average light intensity illuminating the attached Chlorella vulgaris biofilm in the SHPW-PBR was elevated by 204.11% and contributed to a 145.20% improvement on areal C. vulgaris biofilm production. Thereafter, responses of attached C. vulgaris biofilm growth in the SHPW-PBR to various light intensities were evaluated and the maximum areal C. vulgaris biofilm density reached 90.43 g m(-2) under the light intensity of 136 mu mol m(-2) s(-1) after 9 days cultivation. Furthermore, the SHPW-PBR can be easily scaled-up by increasing the quantity of the stacked planar waveguide modules and thus shows great potential in biofilm-based biomass production. (C) 2020 Elsevier B.V. All rights reserved.