Catalysis by Enzymes: The Biological Ammonia Synthesis

Enzymes are nature’s own catalysts and fundamental for life, as they catalyze essentially all biological processes. Compared to inorganic catalysts, however, their structure and function is immensely more complicated. Computational modeling has played an increasing role in elucidating enzyme mechanisms, as it can provide information complementary to experimental techniques. Elucidating enzyme structure and mechanism is not only important to understand the basic functions of life, they can also help to find and develop inorganic catalysts. In this review, an overview of recent computational developments for the enzyme nitrogenase will be given. Nitrogenase catalyzes ammonia synthesis, which is also a very important reaction in inorganic catalysis, and insight on enzyme structure and function could provide understanding on how to design biomimetic catalysts for low temperature ammonia synthesis.     

Infants' understanding of the link between visual perception and emotion: "If she can't see me doing it, she won't get angry."

Two experiments investigated 18-month-olds' understanding of the link between visual perception and emotion. Infants watched an adult perform actions on objects. An emoter then expressed neutral affect or anger toward the adult in response to the adult's actions. Subsequently, infants were given 20 s to interact with each object. In Experiment 1, the emoter faced infants with a neutral expression during each 20-s response period but looked at either a magazine or the infant. In Experiment 2, the emoter faced infants with a neutral expression, and her eyes were either open or closed. When the emoter visually monitored infants' actions, the infants regulated their object-directed behavior on the basis of their memory of the emoter's affect. However, if the previously angry emoter read a magazine (Experiment 1) or closed her eyes (Experiment 2), infants were not governed by her prior emotion. Infants behaved as if they expected the emoter to get angry only if she could see them performing the actions. These findings suggest that infants appreciate how people's visual experiences influence their emotions and use this information to regulate their own behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Optimization of ordered plasmid assembly by gap repair in Saccharomyces cerevisiae

Combinatorial genetic libraries are powerful tools for diversifying and optimizing biomolecules. The process of library assembly is a major limiting factor for library complexity and quality. Gap repair by homologous recombination in Saccharomyces cerevisiae can facilitate in vivo assembly of DNA fragments sharing short patches of sequence homology, thereby supporting generation of high‐complexity libraries without compromising fidelity. In this study, we have optimized the ordered assembly of three DNA fragments into a gapped vector by in vivo homologous recombination. Assembly is achieved by co‐transformation of the DNA fragments and the gapped vector, using a modified lithium acetate protocol. The optimal gap‐repair efficiency is found at a 1:80 molar ratio of gapped vector to each of the three fragments. We measured gap‐repair efficiency in different genetic backgrounds and observed increased efficiency in mutants carrying a deletion of the SGS1 helicase‐encoding gene. Using our experimental conditions, a gap‐repair efficiency of > 10⁶ plasmid‐harbouring colonies/µg gapped vector DNA is obtained in a single transformation, with a recombination fidelity > 90%. Copyright © 2012 John Wiley & Sons, Ltd.     

Commercial Mineral Enhanced Dairy By‐Products as Sodium Replacers,Antioxidants and Calcium Fortifiers in Sausages

Sausages are perceived as high in Na and with a too high Na:K ratio. Frankfurter type sausages are regarded as important contributors of sodium in the diet and thereby of health risks. Surplus products from the dairy industry are various mineral powders enriched in either potassium, calcium, or phosphate and include various amounts of lactose. Sausages were produced at 3 sodium levels (equivalent to 13, 15, and 17 g NaCl/kg sausage) using 4 different milk ingredients (a dried skimmed milk powder, a calcium enriched milk powder, a potassium enriched powder, and a lactose enriched powder). The sausages with added calcium and potassium enriched milk powders resulted in the hardest sausages when compared at the same sodium level. Milk mineral addition also produced whiter and less red sausages. No effect on rancidity after 6 wk at chill (4 °C) storage was observed by adding milk minerals, when compared with adding dried skimmed milk powder. A significant advantage of using these milk minerals in sausages is that the Na:K ratio can be reduced from an unhealthy (in this study 36) to a far healthier ratio ( ? 2) with limited or no taste changes. High additions of milk calcium (6 g/kg), where Ca‐phosphates prevail, added as milk mineral, had no influence on sensory bitterness or aftertaste as typically observed for CaCl₂ additions. Ca additions to sausages are presently presumed to be an advantage with respect to human nutrition.     

Diacylglycerol synthesis by enzymatic glycerolysis: Screening of commercially available lipases

Seven lipases were screened for their ability to synthesize DAG in the glycerolysis of rapeseed oil. In batch reactions with free glycerol, the lipase carrier was of great importance for catalysis. Catalysis did not take place in reactions with lipases having hydrophilic carriers. The best DAG yield (approx. 60 wt%) was achieved with Novozym 435 and Lipase PS-D after 7 h, and an equilibrium was obtained. Stepwise addition of glycerol allowed catalysis with Novozym CALB L (immobilized) to take place in spite of the hydrophilic carrier; however, the DAG yield was only 19 wt%. This result suggests that glycerol forms a layer around the hydrophilic lipase particles, limiting contact between the lipases and the hydrophobic oil phase. With glycerol absorbed on silica gel, all lipases catalyzed the glycerolysis reaction. Faster conversion of TAG was obtained with Lipase PS-D, Lipase AK, and Lipase F-AP15 than in reactions with free glycerol, but the DAG yield remained approximately 60–65 wt%. Nonspecific lipases yielded more 1,3-DAG early in the reaction.     

Supportive relationships in later life.

Adopted a multidimensional approach to the study of the social support convoys of older adults. We distinguished between age and gender differences in 4 specific dimensions of the social support convoy: (a) existence vs functioning of relationships in the convoy, (b) kinds of relationships (i.e., those with children, siblings, friends), (c) types of social support (i.e., emotional support, respect, health support), and (d) receipt vs provision of support. Ss were 718 adults. We found that older people received less support (i.e., emotional and health support) in the absence of sibling relationships. Otherwise, the effects of aging had more to do with what the older person contributed to the convoy than with what he or she received. Women had better social support resources than men, particularly within friendships. We found no evidence, however, that women's social support advantage counterbalanced the effects of aging on the convoy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A SAS-macro for estimation of the cumulative incidence using Poisson regression

In survival analyses, we often estimate the hazard rate of a specific cause. Sometimes the main focus is not the hazard rates but the cumulative incidences, i.e., the probability of having failed from a specific cause prior to a given time. The cumulative incidences may be calculated using the hazard rates, and the hazard rates are often estimated by the Cox regression. This procedure may not be suitable for large studies due to limited computer resources. Instead one uses Poisson regression, which approximates the Cox regression. Rosth?j et al. presented a SAS-macro for the estimation of the cumulative incidences based on the Cox regression. I present the functional form of the probabilities and variances when using piecewise constant hazard rates and a SAS-macro for the estimation using Poisson regression. The use of the macro is demonstrated through examples and compared to the macro presented by Rosth?j et al.     

Immunomodulatory activity of dietary fiber: arabinoxylan and mixed-linked Beta-glucan isolated from barley show modest activities in vitro

High intake of dietary fiber is claimed to protect against development of colorectal cancer. Barley is a rich source of dietary fiber, and possible immunomodulatory effects of barley polysaccharides might explain a potential protective effect. Dietary fiber was isolated by extraction and enzyme treatment. A mixed-linked β-glucan (WSM-TPX, 96.5% β-glucan, Mw 886 kDa), an arabinoxylan (WUM-BS-LA, 96.4% arabinoxylan, Mw 156 kDa), a mixed-linked β-glucan rich fraction containing 10% arabinoxylan (WSM-TP) and an arabinoxylan rich fraction containing 30% mixed-linked β-glucan (WUM-BS) showed no significant effect on IL-8 secretion and proliferation of two intestinal epithelial cell lines, Caco-2 and HT-29, and had no significant effect on the NF-κB activity in the monocytic cell line U937-3κB-LUC. Further enriched arabinoxylan fractions (WUM-BS-LA) from different barley varieties (Tyra, NK96300, SB94897 and CDCGainer) were less active than the mixed-linked β-glucan rich fractions (WSM-TP and WSM-TPX) in the complement-fixing test. The mixed-linked β-glucan rich fraction from NK96300 and CDCGainer showed similar activities as the positive control while mixed-linked β-glucan rich fractions from Tyra and SB94897 were less active. From these results it is concluded that the isolated high molecular weight mixed-linked β-glucans and arabinoxylans from barley show low immunological responses in selected in vitro test systems and thus possible anti-colon cancer effects of barley dietary fiber cannot be explained by our observations.     

Emissions of ultrafine particles from five types of candles during steady burn conditions

Emissions from candles are of concern for indoor air quality. In this work, five different types of pillar candles were burned under steady burn conditions in a new laboratory scale system for repeatable and controlled comparison of candle emissions (temperature ~25°C, relative humidity ~13%, O₂ >18%, air exchange rate 1.9 h⁻¹). Burn rate, particle number concentrations, mass concentrations, and mode diameters varied between candle types. Based on the results, the burning period was divided in two phases: initial (0–1 h) and stable (1–6 h). Burn rates were in the range 4.4–7.3 and 4.7–7.1 g/h during initial and stable phase, respectively. Relative particle number emissions, mode diameters, and mass concentrations were higher during the initial phase compared to the stable phase for a majority of the candles. We hypothesize that this is due to elevated emissions of wick additives upon ignition of the candle together with a slightly higher burn rate in the initial phase. Experiments at higher relative humidity (~40%) gave similar results with a tendency toward larger particle sizes at the higher relative humidity. Chemical composition with respect to inorganic salts was similar in the emitted particles (dry conditions) compared to the candlewicks, but with variations between different candles.