Bacterial β-peptidyl aminopeptidases: on the hydrolytic degradation of β-peptides

The special chemical and biological features of β-peptides have been investigated intensively during recent years. Many studies emphasize the restricted biodegradability and the high metabolic stability of this class of compounds. β-Peptidyl aminopeptidases form the first family of enzymes that hydrolyze a variety of short β-peptides and β-amino-acid-containing peptides. All representatives of this family were isolated from Gram-negative bacteria. The substrate specificities of the peptidases vary greatly, but the enzymes have common structural properties, and a similar reaction mechanism can be expected. This review gives an overview on the β-peptidyl aminopeptidases with emphasis on their biochemical and structural properties. Their possible physiological function is discussed. Functionally and structurally related enzymes are compared to the β-peptidyl aminopeptidase

Overproduction and characterization of a recombinant D -amino acid oxidase from Arthrobacter protophormiae

A screening of soil samples for d-amino acid oxidase (d-AAO) activity led to the isolation and identification of the gram-positive bacterium Arthrobacter protophormiae. After purification of the wild-type d-AAO, the gene sequence was determined and designated dao. An alignment of the deduced primary structure with eukaryotic d-AAOs and d-aspartate oxidases showed that the d-AAO from A. protophormiae contains five of six conserved regions; the C-terminal type 1 peroxisomal targeting signal that is typical for d-AAOs from eukaryotic origin is missing. The dao gene was cloned and expressed in Escherichia coli. The purified recombinant d-AAO had a specific activity of 180U mg protein−1 for d-methionine and was slightly inhibited in the presence of l-methionine. Mainly, basic and hydrophobic d-amino acids were oxidized by the strictly enantioselective enzyme. After a high cell density fermentation, 2.29 × 106U of d-AAO were obtained from 15l of fermentation brot

Beschreibung von computergestütztenLernumgebungen in der Medizin unter besonderer Berücksichtigung von Qualitätsmerkmalen

Durch die hohe Verbreitung des Internets in den letzten Jahren haben sich die Einsatzmöglichkeiten von computerunterstützten medizinischen Lernumgebungen stark verändert. Es wurde eine Vielzahl von webbasierten Lernumgebungen entwickelt und sehr häufig kostenfrei Studierenden und anderen Interessierten angeboten. Nach anfänglich großer Euphorie über die Vorteile des Web kristallisierten sich diverse Probleme heraus. So stellt sich die Frage, welche Informationen über eine Lernumgebung verfügbar sind und wie man dieses strukturieren kann. Insbesondere ist zu klären, wie man die Qualität einer Lernumgebung erfassen und dem Nutzer zugänglich machen kann. Das Ziel dieser Arbeit ist daher die Erarbeitung eines Beschreibungsrahmens für medizinische Lernumgebungen im Web unter besonderer Berücksichtigung der Ausarbeitung von Qualitäts-merkmalen. Die Frage, wie Lernumgebungen bezüglich ihrer Qualität unterschieden werden können, wurde anhand von verschiedenen Auswahlinstrumenten untersucht, die Lernumgebungen mittels Qualitäts-kriterien bewerten. Eine Bewertung dieser Kriterienkataloge ergab, dass sowohl ihre Validität als auch ihre Reliabilität zu gering für eine verlässliche Aussage ist. Insbesondere berücksichtigen sie den Einsatzkontext der Lernumgebung nur unzureichend. Auch die existierenden Ansätze zur Bewertung von medizinischen Websites sind nicht ausreichend, da sie in der Regel didaktische Kriterien vermissen lassen. Der Vergleich und die anschließende Bewertung verschiedener Beschreibungsstandards (Metadaten) ergab, dass sich Learning Object Metadata (LOM) am besten als Standard für die Beschreibung von Lernumgebungen eignet. Aus den zur Verfügung stehenden neun Kategorien des LOM-Standards konnten 16 Qualitäts-merkmale identifiziert werden. Diese wurden mit 13 weiteren Qualitätsmerkmalen in eine erweiterte Form des LOM-Standards zusammengeführt. Der eigene Ansatz bietet zusätzliche Metadaten zu Qualitätsmanage-ment, Evaluation und Nutzererfahrungen. Die erweiterte Form des LOM-Standards wurde in ein Datenmodell überführt; dazu diente der LOM-Standard in der Implementierung des IMS Learning Resource Meta-data XML Binding als Basis. Der Einsatz von XML erleichterte die anschließende exemplarische Umsetzung als Webanwendung und gewährleistet die Interoperabilität mit externen Systemen. Die Anwendung, der Learning Resource Server Medizin (LRSMed), bietet dem Nutzer flexible und effiziente Möglichkeiten, aus neun Suchkriterien mit vorgegebenem Vokabular in Verbindung mit einer Volltextsuche adäquate Lernumgebungen zu finden. Die Bewertung der Ergeb-nisse bleibt ihm selbst überlassen, da diese ohne Kenntnis des situativen Kontextes kaum möglich ist. Die Herkunft der Metadaten ist für den Nutzer transparent, da er Informationen zur Quelle erhält. Insgesamt kann der Schluss gezogen werden, dass der Nutzer durch die Erweiterungen des LOM-Standards und deren Implementierung in Form des LRSMed bei der Recherche nach medizinischen, webbasierten und derzeit frei verfügbaren Lernumgebungen unterstützt werden kann. Für einen entsprechenden Nachweis ist die Evaluation des LRSMed anzustreben. Inwiefern Lernumgebungen in Zukunft noch kostenfrei zur Verfügung stehen, ist offen, da insbesondere im medizinischen Bereich multimediales Material aufwändig aufbereitet werden muss

Molekulares Profil und phänotypische Analyse von enterohämorrhagischen und enteropathogenen Escherichia coli der Serogruppe O26

Enterohämorrhagische Escherichia coli (EHEC) und atypische enteropathogene Escherichia coli (aEPEC) gelten weltweit als Auslöser von Durchfallerkrankungen. EHEC können darüber hinaus das hämolytisch-urämische Syndrom (HUS) verursachen. Ein Unterscheidungskriterium zwischen EHEC und aEPEC ist die Fähigkeit zur Shiga Toxin-Produktion. Im Gegensatz zu typischen EPEC fehlt den aEPEC das EAF-Plasmid. Im Rahmen dieser Arbeit wurden EHEC und aEPEC der Serogruppe O26 molekularbiologisch und phänotypisch charakterisiert. Die Ergebnisse dieser Untersuchungen zeigen, dass beide Pathogruppen EHEC-Hämolysin produzieren und gegenüber Tellurit resistent sind. Die E. coli O26 Stämme waren nicht in der Lage Rhamnose zu fermentieren. Sowohl aEPEC als auch EHEC beherbergten das für Intimin kodierende eae-betta-Gen und trugen, unabhängig von ihrer Beweglichkeit, das für Flagellin kodierende fliCH11- Gen. Zudem zeigt sich, dass weitere potentielle Virulenzfaktoren in EHEC und aEPEC O26 vorkommen

Unpacking the complexity of the polyethylene food contact articles value chain: A chemicals perspective

Polyethylene (PE) is the most widely used type of plastic food packaging, in which chemicals can potentially migrate into packaged foods. The implications of using and recycling PE from a chemical perspective remain underexplored. This study is a systematic evidence map of 116 studies looking at the migration of food contact chemicals (FCCs) across the lifecycle of PE food packaging. It identified a total of 377 FCCs, of which 211 were detected to migrate from PE articles into food or food simulants at least once. These 211 FCCs were checked against the inventory FCCs databases and EU regulatory lists. Only 25% of the detected FCCs are authorized by EU regulation for the manufacture of food contact materials. Furthermore, a quarter of authorized FCCs exceeded the specific migration limit (SML) at least once, while one-third (53) of non-authorised FCCs exceeded the threshold value of 10 μg/kg. Overall, evidence on FCCs migration across the PE food packaging lifecycle is incomplete, especially at the reprocessing stage. Considering the EU's commitment to increase packaging recycling, a better understanding and monitoring of PE food packaging quality from a chemical perspective across the entire lifecycle will enable the transition towards a sustainable plastics value chain

Hazardous chemicals in recycled and reusable plastic food packaging

In the battle against plastic pollution, many efforts are being undertaken to reduce, reuse and recycle plastics. If tackled in the right way, these efforts have the potential to contribute to reducing plastic waste and plastic’s spread in the environment. However, reusing and recycling plastics can also lead to unintended negative impacts because hazardous chemicals, like endocrine disrupters and carcinogens, can be released during reuse and accumulate during recycling. In this way, plastic reuse and recycling become vectors for spreading chemicals of concern. This is especially concerning when plastics are reused for food packaging, or when food packaging is made with recycled plastics. Therefore, it is of utmost importance that care is taken to avoid hazardous chemicals in plastic food contact materials (FCMs) and to ensure that plastic packaging that is reused or made with recycled content is safe for human health and the environment. The data presented in this review are obtained from the Database on Migrating and Extractable Food Contact Chemicals (FCCmigex), which is based on over 800 scientific publications on plastic FCMs. We provide systematic evidence for migrating and extractable food contact chemicals (FCCs) in plastic polymers that are typically reused, such as polyamide (PA), melamine resin, polycarbonate and polypropylene, or that contain recycled content, such as polyethylene terephthalate (PET). A total of 1332 entries in the FCCmigex database refer to the detection of 509 FCCs in repeat-use FCMs made of plastic, and 853 FCCs are found in recycled PET, of which 57.6% have been detected only once. Here, we compile information on the origin, function and hazards of FCCs that have been frequently detected, such as melamine, 2,4-di-tert-butylphenol, 2,6-di-tert-butylbenzoquinone, caprolactam and PA oligomers and highlight key knowledge gaps that are relevant for the assessment of chemical safety

Overview of intentionally used food contact chemicals and their hazards

Food contact materials (FCMs) are used to make food contact articles (FCAs) that come into contact with food and beverages during, e.g., processing, storing, packaging, or consumption. FCMs/FCAs can cause chemical contamination of food when migration of their chemical constituents (known as food contact chemicals, FCCs) occurs. Some FCCs are known to be hazardous. However, the total extent of exposure to FCCs, as well as their health and environmental effects, remain unknown, because information on chemical structures, use patterns, migration potential, and health effects of FCCs is often absent or scattered across multiple sources. Therefore, we initiated a research project to systematically collect, analyze, and publicly share information on FCCs. As a first step, we compiled a database of intentionally added food contact chemicals (FCCdb), presented here. The FCCdb lists 12′285 substances that could possibly be used worldwide to make FCMs/FCAs, identified based on 67 FCC lists from publicly available sources, such as regulatory lists and industry inventories. We further explored FCCdb chemicals’ hazards using several authoritative sources of hazard information, including (i) classifications for health and environmental hazards under the globally harmonized system for classification and labeling of chemicals (GHS), (ii) the identification of chemicals of concern due to endocrine disruption or persistence related hazards, and (iii) the inclusion on selected EU- or US-relevant regulatory lists of hazardous chemicals. This analysis prioritized 608 hazardous FCCs for further assessment and substitution in FCMs/FCAs. Evaluation based on non-authoritative, predictive hazard data (e.g., by in silico modeling or literature analysis) highlighted an additional 1411 FCCdb substances that could thus present similar levels of concern, but have not been officially classified so far. Lastly, for over a quarter of all FCCdb chemicals no hazard information could be found in the sources consulted, revealing a significant data gap and research need.MAVA Foundation; Valery Foundatio

Unpacking the complexity of the polyethylene food contact articles value chain: A chemicals perspective

Polyethylene (PE) is the most widely used type of plastic food packaging, in which chemicals can potentially migrate into packaged foods. The implications of using and recycling PE from a chemical perspective remain underexplored. This study is a systematic evidence map of 116 studies looking at the migration of food contact chemicals (FCCs) across the lifecycle of PE food packaging. It identified a total of 377 FCCs, of which 211 were detected to migrate from PE articles into food or food simulants at least once. These 211 FCCs were checked against the inventory FCCs databases and EU regulatory lists. Only 25% of the detected FCCs are authorized by EU regulation for the manufacture of food contact materials. Furthermore, a quarter of authorized FCCs exceeded the specific migration limit (SML) at least once, while one-third (53) of non-authorised FCCs exceeded the threshold value of 10 μg/kg. Overall, evidence on FCCs migration across the PE food packaging lifecycle is incomplete, especially at the reprocessing stage. Considering the EU’s commitment to increase packaging recycling, a better understanding and monitoring of PE food packaging quality from a chemical perspective across the entire lifecycle will enable the transition towards a sustainable plastics value chain.The authors would like to express their gratitude to the Food Packaging Forum (FPF) for their support in compiling this systematic evidence map. This study was funded by Brunel University London as part of the Brunel Research Initiative & Enterprise Fund (BRIEF) award No. 11683100 , in the context of the ' Closing the Plastic Food Packaging Loop ' project.Scopu