Studies on the formation of lysinomethylalanine and histidinomethylalanine in milk products

From reaction mixtures consisting ofN-acetyldehydroaminobutyric acid methyl ester andN -acetyl-l-lysine orN -acetyl-l-histidine, respectively, distinct amounts of the cross-link amino acidsN -(2-amino-2-carboxy-l-methylethyl)-l-lysine (lysinomethylalanine, LMeAL) andN -(2-amino-2-carboxy-1-methyl-ethyl)-l-histidine (histidinomethylalanine, HMeAL) were isolated via preparative ion-exchange chromatography and identified by¹H- and¹³C-nuclear magnetic resonance. In the amino acid chromatogram, both compounds eluted clearly separated from other basic amino acids. However, neither LMeAL nor HMeAL could be detected in numerous acid hydrolysates of a range of milk products. In model studies, threonine showed a significantly lower tendency for an alkali-induced -elimination reaction compared to serine. The reactivity of the resulting dehydroaminobutyric acid towards nucleophiles was more than tenfold lower as compared to dehydroalanine. Thus, the formation of LMeAL as well as of HMeAL during food processing is negligible.

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Studien zur Bildung von Lysinomethylalanin und Histidinomethylalanin in Milchprodukten

Zusammenfassung Aus Reaktionsansätzen bestehend ausN-Acetyldehydroaminobuttersäurenthylester undN -Acetyl-l-lysin beziehungsweiseN -Acetyl-l-histidin konnten die Crosslink-AminosäurenN -(2-Amino-2-carboxy-1-methyl-ethyl)-l-lysin (Lysinomethylalanin, LMeAL) undN -(2 amino-2-carboxy-2 -methyl-ethyl)-l-histidin (Histidinomethylalanin, HMeAL) durch präparative Ionenaustauschchromatographie isoliert und anschließend durch 1H-und¹³C-NMR identifiziert werden. Das Aminosäurechromatogramm zeigte eine eindeutige Trennung beider Aminosäurederivate von anderen basischen Aminosäuren. Dennoch konnten in einer großen Zahl von Säurehydrolysaten der verschiedensten Milchprodukte weder LMeAL noch HMeAL nachgewiesen werden. In Modelluntersuchungen erfolgte die -Elimination an Threonin im Vergleich zu Serin in einem deutlich geringeren Maße. Die Reaktivität der dabei entstehenden Dehydroaminobuttersäure gegenüber Nucleophilen war mehr als zehnfach geringer als die von Dehydroalanin. Damit kann die Bildung sowohl von LMeAL als auch von HMeAL bei der Verarbeitung von Nahrungsmitteln als vernachlässigbar gering eingeschätzt werden.

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Dedicated to Prof. Dr. W. Baltes on the occasion of his 65th birthday     

Strain hardening and instability in biaxially streched sheets

This work is concerned with the origins of the two different patterns of failure limits in biaxially stretched sheets which were recently described in Ref. 1: the brass-type in which the limit strain is insensitive to strain state, and that of ferritic steel in which the limit strain increases as the imposed strain-ratio, ρ = ε₂/ε₁, changes from zero (plane-strain tension) toward unity (balanced biaxial tension). An earlier proposal that different slip modes,i.e. wavy in ferrite vs planar in brass, might have contributed to these failurelimit differences was found not to be valid. There were two parts to the main experimental program: the prestraining of small sheets by proportional loading on different paths betweenρ = 0 andρ = 1, followed by tension testing, and a more direct measurement of strain hardening and instability between ρ ≅ — 1/2 (uniaxial tension) andρ = 0. The principal finding was that the overall hardening rate, essentially as it appeared in the material’s effective stress-strain curve, changed with the loading path. Inα brass it decayed as p was increased from ∼—1/2 to 1; in ferritic steel it increased; and in aluminum it was affected very little. Such changes in hardening rate cause similar changes in the material’s capacity for stable flow. The stable flow, in turn, is the base to which a quasistable-flow increment (whenρ is >0) is added in reaching the observed failure limit. Thus a base ofρ-dependent height can account for the failure-limit patterns. There is still no explanation for the ρ dependence of the hardening rate. AMIT K. GHOSH, formerly Graduate Student, Massachusetts Institute of Technology, Cambridge, Mass. 02139, This paper is based upon a thesis submitted by AMIT K. GHOSH in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology.     

The origin of strain-rate sensitivity in OFHC copper

This investigation was conducted to determine the nature of the strain-rate sensitivity of OFHC copper at room temperature. In particular, the relative magnitudes of the dynamic contribution (particle inertia, suppression of thermal assistance, and so forth) and the nondynamic contribution (namely, the accelerated rate of strain hardening observed at high strain rates) to the strain-rate sensitivity were determined. Specimens were dynamically compressed using the Hopkinson pressure bar technique, and then were reloaded quasistatically to determine their respective yield strengths. The dynamic contribution to strainrate sensitivity was taken as the difference between the peak dynamic flow stress and the flow stress of the same specimen when reloaded quasistatically. The nondynamic contribution to strain-rate sensitivity of the flow stress was taken as the difference between the quasistatic flow stress in reloading of a specimen prestrained ε₀ dynamically and the flow stress at ε₀ for a sample deformed in uniaxial quasistatic compression. The room temperature dynamic flow-stress of OFHC copper, deformed at 500s⁻¹, was found to be 25 pct higher than the conventional quasistatic flow stress for this metal over a strain range of 0.08 to 0.20. The nondynamic contribution to strain-rate sensitivity was found to be about 60 pct of the total flow stress increase and has been attributed to a difference in strainhardening at different strain rates. Thus, it appears that in OFHC copper at room temperature and at strain rates of about 500s⁻¹, the nondynamic contribution to strain-rate sensitivity is more significant than the dynamic contribution.     

Facing the issues.

Replies to P. L. Wachtel (see PA, Vol. 51:Issue 5) stating that efforts to achieve integration between psychodynamic and behavioral approaches are appealing, but are unlikely to succeed unless the empirical issues are faced without distortion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Water Resources: The Delaware Basin

Philadelphia is in competition with New York City and Baltimore in staking a claim for the water resources it will need in the next half century and beyond. A new governmental organization having a delegation of both state and federal powers for continuous planning and for unified management and control of the water resources of the entire Delaware River Basin has been proposed; and a federal-state compact for its establishment is being negotiated.     

Photo-vulcanization using thiol-ene chemistry: Film formation,morphology and network characteristics of UV crosslinked rubber latices

The photo-vulcanization with versatile thiol-ene chemistry represents an innovative approach to crosslink diene-rubber materials both in latex and in solid film state. In this work, the structure of elastomer-based thiol-ene networks and the morphology after film formation are studied in detail using electron microscopic techniques, atomic force microscopy and multiple-quantum solid-state NMR spectroscopy. Additionally, film formation properties and corresponding macroscopic properties of photo-vulcanized natural rubber (NR) latex and its synthetic counterpart, isoprene rubber (IR) latex, are determined in dependence on the curing procedure (pre- and post-vulcanization). The results reveal that thiol-ene cured elastomers comprise homogenously distributed crosslinks with a low amount of short chain defects. Whilst photochemically pre-cured NR latex particles provide coherent films, the film formation and mechanical properties of IR are strongly governed by the crosslink density of the latex particles. In film state, photo-vulcanization promotes narrow crosslink distributions and excellent tensile properties of both NR and IR.     

Brassica Plant Responses to Mild Herbivore Stress Elicited by Two Specialist Insects from Different Feeding Guilds

Compensation growth and chemical defense are two components of plant defense strategy against herbivores. In this study, compensation growth and the response of primary and secondary metabolites were investigated in Brassica rapa plants subjected to infestation by two herbivores from contrasting feeding guilds, the phloem-feeding aphid Brevicoryne brassicae and the leaf-feeding caterpillar Pieris brassicae. These specialist herbivores were used at two different densities and allowed to feed for seven days on a young caged leaf. Changes in growth rates were assessed for total leaf area and bulb mass, whereas changes in primary and secondary metabolites were evaluated in young and mature leaves, roots, and bulbs. Mild stress by caterpillars on young plants enhanced mean bulb mass and elicited a contrasting regulation of aliphatic and indolic glucosinolates in the leaves. In contrast, mild stress by aphids enhanced leaf growth and increased glucosinolate concentrations in the bulb, the most important storage organ of B. rapa. A similar mild stress by either herbivore to older plants did not alter plant growth parameters or concentrations of the metabolites analyzed. In conclusion, Brassica plant growth was either maintained or enhanced under mild herbivore stress, and defense patterns differed strongly in response to herbivore type and plant development stage. These results have implications for the understanding of plasticity in plant defenses against herbivores and for the management of Brassica rapa in agroecosystems.     

Thin-film solar cells

The R&D status of cells and modules based on hydrogenated amorphous silicon (a-Si:H) and those based on CdTe and CuInSe₂ is reviewed. The stability of a-Si:H solar cells is still a major concern. Improvements have been achieved on an empirical basis by application of multijunction structures, optimization of interfaces, etc. Stabilized efficiencies of close to 10% have been reported. In parallel, the introduction of the ‘defect-pool model’ led to remarkable progress in understanding; it follows that a-SiGe:H instead of a-Si:H should be used for the i-layer (absorber). Improved cell engineering concepts, however, such as enhancement of the built-in electric field via reduction of the i-layer thickness and/or folded structures, are believed to be more promising. Polycrystalline thin-film cells based on CdTe and CuInSe₂ are not affected by inherent degradation mechanisms. the specific properties of these materials demand heterojunctions, and particular problems arise due to the polycrystallinity of the films and to the lattice mismatch and mismatch of the electronic band structures of the materials involved. These are discussed in conjunction with measures currently applied for optimizing solar cell performance. Both cell types exhibit eficiencies in the range 16-17%. Estimations of production costs and energy payback times of thin-film photovoltaic modules are reviewed (even below 1 US$ W_p⁻¹ and as low as 4 months, respectively) and environmental concerns, especially for Cd-containing cells, are summarized.     

Functional Characterization of the Solute Carrier LAT-1 (SLC7A5/SLC2A3) in Human Brain Capillary Endothelial Cells with Rapid UPLC-MS/MS Quantification of Intracellular Isotopically Labelled L-Leucine

The solute carrier L-type amino acid transporter 1 (LAT-1/SLC7A5) is a viable target for drug delivery to the central nervous system (CNS) and tumors due to its high abundance at the blood–brain barrier and in tumor tissue. LAT-1 is only localized on the cell surface as a heterodimer with CD98, which is not required for transporter function. To support future CNS drug-delivery development based on LAT-1 targeting, we established an ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) assay for stable isotopically labeled leucine ([¹³C₆, ¹⁵N]-L-leucine), with a dynamic range of 0.1–1000 ng/mL that can be applied for the functional testing of LAT-1 activity when combined with specific inhibitors and, consequently, the LAT-1 inhibition capacity of new compounds. The assay was established in a 96-well format, facilitating high-throughput experiments, and, hence, can support the screening for novel inhibitors. Applicable recommendations of the US Food and Drug Administration and European Medicines Agency for bioanalytical method validation were followed to validate the assay. The assay was applied to investigate the IC₅₀ of two well-known LAT-1 inhibitors on hCMEC/D3 cells: the highly specific LAT-1 inhibitor JPH203, which was also used to demonstrate LAT-1 specific uptake, and the general system L inhibitor BCH. In addition, the [¹³C₆, ¹⁵N]-L-leucine uptake was determined on two human brain capillary endothelial cell lines (NKIM-6 and hCMEC/D3), which were characterized for their expressional differences of LAT-1 at the protein and mRNA level and the surface amount of CD98. The IC₅₀ values of the inhibitors were in concordance with previously reported values. Furthermore, the [¹³C₆, ¹⁵N]-L-leucine uptake was significantly higher in hCMEC/D3 cells compared to NKIM-6 cells, which correlated with higher expression of LAT-1 and a higher surface amount of CD98. Therefore, the UPLC-MS/MS quantification of ([¹³C₆, ¹⁵N]-L-leucine is a feasible strategy for the functional characterization of LAT-1 activity in cells or tissue.