Biochemical characterization and synthetic application of aromatic L-amino acid decarboxylase from Bacillus atrophaeus.

Aromatic L-amino acid decarboxylases (AADCs) are ubiquitously found in higher organisms owing to their physiological role in the synthesis of neurotransmitters and alkaloids. However, bacterial AADC has not attracted much attention because of its rather limited availability and narrow substrate range. Here, we examined the biochemical properties of AADC from Bacillus atrophaeus (AADC-BA) and assessed the synthetic feasibility of the enzyme for the preparation of monoamine neurotransmitters. AADC-BA was expressed in Escherichia coli BL21(DE3) and the purified enzyme showed a specific activity of 2.6 ± 0.4 U/mg for 10 mM L-phenylalanine (L-Phe) at 37 °C. AADC-BA showed optimal pH and temperature ranges at 7-8 and 37-45 °C, respectively. The KM and kcat values for L-Phe were 7.2 mM and 7.4 s-1, respectively, at pH 7.0 and 37 °C. Comparison of the kinetic constants at different temperatures revealed that the temperature dependency of the enzyme was mainly determined by catalytic turnover rather than substrate binding. AADC-BA showed a broad substrate scope for various aromatic amino acids, including L-Phe, L-tryptophan (610% relative to L-Phe), L-tyrosine (12%), 3,4-dihydroxyphenyl-L-alanine (24%), 5-hydroxy-L-tryptophan (L-HTP, 71%), 4-chloro-L-phenylalanine (520%), and 4-nitro-L-phenylalanine (450%). Homology modeling and docking simulations were carried out and were consistent with the observed substrate specificity. To demonstrate the synthetic potential of AADC-BA, we carried out the production of serotonin by decarboxylation of L-HTP. The reaction yield of serotonin reached 98% after 1 h at the reaction conditions of 50 mM L-HTP and 4 U/mL AADC-BA. Moreover, we carried out preparative-scale decarboxylation of L-Phe (100 mM in 40-mL reaction mixture) and isolated the resulting 2-phenylethylamine (51% recovery yield). We expect that the broad substrate specificity of AADC-BA can be exploited to produce various aromatic biogenic amines. KEY POINTS: • AADC-BA showed broad substrate specificity for various aromatic amino acids. • The substrate specificity was elucidated by in silico structural modeling. • The synthetic potential of AADC-BA was demonstrated for the production of biogenic amines.

Diurnal and Seasonal Variations in the Effect of Urban Environmental Factors on Air Temperature: A Consecutive Regression Analysis Approach.

This study investigates the diurnal and seasonal variations in the effect of environmental features on air temperature in Seoul, Korea. We expect that this study will lead to the identification of factors that can be applied for urban heat island mitigation strategies in summer without leading to an unintended result in winter. As our dependent variable, we employed the smoothed 31-day moving average of air temperatures, where we controlled the seasonal variation by normalizing the values observed from 247 automatic weather stations (AWS) from 2015 to 2016. Subsequently, we conducted consecutive log-log regression analyses of each day to examine patterns of change in regression coefficients and the significance of each independent variable. For independent variables, we applied built environment features including albedo, land-use, average building floors, the sky view factor, and green and water areas. This study provides analytical results regarding the relationship between environmental factors and air temperature. This study also addresses imperative issues for planners, especially regarding albedo, wind path, building geometry, and land use types. Finally, this study gives useful insights for managing the diurnal and seasonal variations of urban thermal environment in the mega-city.

Antioxidant activity and bioaccessibility of size-different nanoemulsions for lycopene-enriched tomato extract.

Lycopene nanoemulsions were prepared to protect the antioxidant activity and improve the bioaccessibility of lycopene-enriched tomato extract (containing 6% of lycopene) by an emulsification-evaporation method. Lycopene nanoemulsions, with droplet sizes between 100 and 200 nm, exhibited higher anti-radical efficiency and antioxidant activity, than did those smaller than 100 nm. Strong protectability of lycopene in droplets smaller than 100 nm was associated with relatively slower rates of DPPH and ABTS reactions. In vitro bioaccessibility values of lycopene-enriched tomato extract, lycopene nanoemulsions with droplets larger than 100 nm (approximately 150 nm on average), and lycopene nanoemulsions with droplets smaller than 100 nm (69 nm on average) were 0.01, 0.53, and 0.77, respectively. Interestingly, nanoemulsions with droplets smaller than 100 nm showed the highest in vitro bioaccessibility, which could be interpreted as evidence of nanoemulsification enhancing the in vitro bioaccessibility of lycopene.

Physiochemical properties and prolonged release behaviours of chitosan-denatured ß-lactoglobulin microcapsules for potential food applications.

Chitosan (CS) and ß-lactoglobulin (ßlg) double-wall coating was designed as a shell structure to achieve prolonged release of core material in the gastrointestinal tract (GI) for potential food applications. A model core material, brilliant blue (BB) dye, was incorporated into CS as the primary wall material, and subsequently, denatured ßlg, a secondary wall material, was used to coat the outer layer. The strongest interaction occurred between 0.5% (w/v) ßlg and 0.5% (w/v) CS at pH 5.5 ± 0.1, where the opposite charges of CS and ßlg formed a complex, which is especially favourable in acidic beverage systems. Under simulated stomach conditions, a denatured-ßlg coat resisted acid conditions and pepsin hydrolysis for 2h. While mimicking small intestine conditions, ßlg was degraded by pancreatin, causing the release of BB-loaded CS to the intestinal fluid at a constant rate. The sustained release of core material later in the GI tract provided an optimal absorption rate in the small intestine.