Untersuchungen zur Rolle der Phosphoenolpyruvat-Carboxykinase und des NADP+-Malat-Enzyms in der filamentösen Phaeophycee Ectocarpus siliculosus

In der filamentösen Braunalge Ectocarpus siliculosus liegen die Enzyme Phosphoenolpyruvat-Carboxykinase (PEPCK) und das NADP+-Malat-Enzym in hohen Aktivitäten vor. Die Beteiligung beider Enzyme an einem für die Alge vorgeschlagenen C4/CAM-Metabolismus wurde fraglich, nachdem zum einen nicht alle der für einen vollständigen Zyklus benötigten Enzyme nachgewiesen werden konnten und zum anderen mögliche Metabolite in vivo in zu geringen Konzentrationen vorlagen, um für den postulierten Speichermetaboliten von CO2 in Frage zu kommen. Daraus ergab sich die Frage nach der zellulären Funktion der Enzyme. Zur Klärung der Funktion sowohl der PEPCK als auch des NADP+-Malat-Enzyms wurden die Enzyme aus E. siliculosus isoliert und gereinigt. Dabei wurde für die native PEPCK eine relative molekulare Masse von 90 kDa ermittelt. Nach Denaturierung in der SDS-PAGE zeigte sich ein 62 kDa- sowie ein prominenteres 18 kDa-Polypeptid. Die relative molekulare Masse des nativen NADP+-Malat-Enzyms wurde mit 440 kDa bestimmt. In der SDS-PAGE zeigte sich ein einzelnes 56 kDa-Polypeptid, und es wurde geschlossen, dass das funktionelle Enzym als Oktamer vorliegt. Für alle der für die Carboxylierungsreaktion der PEPCK benötigten Substrate ergaben sich normale Michaelis-Menten-Kinetiken mit den Km-Werten 1,46 mM (CO2), 0,5 mM (PEP) und 0,23 mM (ADP). Auch für die Decarboxylierungsreaktion des Malat-Enzyms zeigte sich mit Malat eine normale Michaelis-Menten-Kinetik (Km = 0,36 mM). Im Fall des NADP+ wurde das Vorliegen positiver Kooperativität mit einem Hill-Koeffizienten von 2,74 nachgewiesen. Dies deutet darauf hin, daß das Enzym über mindestens drei Bindungsstellen für NADP+ verfügt. Zur Herstellung spezifischer Antikörper gegen beide Enzyme wurden Kaninchen mit den denaturierten Polypeptiden nach der SDS-PAGE immunisiert. Trotz wiederholtem Ansatz und verlängertem Standardimmunisierungsprogramm ergab sich ein geeignetes Antiserum nur für das 18 kDa-Polypeptid der PEPCK. Die IgG-Fraktion dieses Serums reagierte sowohl mit dem 18 kDa- als auch mit dem 62 kDa-Polypeptid der PEPCK, was darauf hindeutet, dass beide Polypeptide Degradationsprodukte eines wahrscheinlich monomeren nativen Polypeptids sind. In Immunlokalisationsstudien mit diesem Antikörper wurde die PEPCK in den Pyrenoiden von E. siliculosus nachgewiesen. Ebenso befindet sich die Rubisco, nachgewiesen mit einem Antikörper gegen das native Enzym aus Spinat, in den Pyrenoiden. Die Lokalisation der PEPCK in direkter Nachbarschaft zur Rubisco schließt erneut die Funktion eines C4-Mechanismus bei E. siliculosus aus. Eine anaplerotische Rolle der PEPCK in den Zellen der Alge ist wahrscheinlich

Ein Buch in sieben Tagen - ein spannendes Projekt mit vielen Facetten

2013 wurde das frei zugängliche "Lehrbuch für Lernen und Lehren mit Technologien“ (L3T 2.0) in sieben Tagen mit über 200 Projektbeteiligten komplett überarbeitet und neu aufgelegt

Die Sammlung Friedrich Schmuck oder die Farben der Nelke.

Kurzporträt eines Sonderbestandes der Hochschulbibliothek der Fachhochschule Köl

Hybrid time-domain and continuous-wave diffuse optical tomography instrument with concurrent, clinical magnetic resonance imaging for breast cancer imaging

Diffuse optical tomography has demonstrated significant potential for clinical utility in the diagnosis and prognosis of breast cancer, and its use in combination with other structural imaging modalities improves lesion localization and the quantification of functional tissue properties. Here, we introduce a hybrid diffuse optical imaging system that operates concurrently with magnetic resonance imaging (MRI) in the imaging suite, utilizing commercially available MR surface coils. The instrument acquires both continuous-wave and time-domain diffuse optical data in the parallel-plate geometry, permitting both absolute assignment of tissue optical properties and three-dimensional tomography; moreover, the instrument is designed to incorporate diffuse correlation spectroscopic measurements for probing tissue blood flow. The instrument is described in detail here. Image reconstructions of a tissue phantom are presented as an initial indicator of the system's ability to accurately reconstruct optical properties and the concrete benefits of the spatial constraints provided by concurrent MRI. Last, we briefly discuss how various data combinations that the instrument could facilitate, including tissue perfusion, can enable more comprehensive assessment of lesion physiology

Multi-modal diffuse optical techniques for breast cancer neoadjuvant chemotherapy monitoring (Conference Presentation)

We present high spatial density, multi-modal, parallel-plate Diffuse Optical Tomography (DOT) imaging systems for the purpose of breast tumor detection. One hybrid instrument provides time domain (TD) and continuous wave (CW) DOT at 64 source fiber positions. The TD diffuse optical spectroscopy with PMT- detection produces lowresolution images of absolute tissue scattering and absorption while the spatially dense array of CCD-coupled detector fibers (108 detectors) provides higher-resolution CW images of relative tissue optical properties. Reconstruction of the tissue optical properties, along with total hemoglobin concentration and tissue oxygen saturation, is performed using the TOAST software suite. Comparison of the spatially-dense DOT images and MR images allows for a robust validation of DOT against an accepted clinical modality. Additionally, the structural information from co-registered MR images is used as a spatial prior to improve the quality of the functional optical images and provide more accurate quantification of the optical and hemodynamic properties of tumors. We also present an optical-only imaging system that provides frequency domain (FD) DOT at 209 source positions with full CCD detection and incorporates optical fringe projection profilometry to determine the breast boundary. This profilometry serves as a spatial constraint, improving the quality of the DOT reconstructions while retaining the benefits of an optical-only device. We present initial images from both human subjects and phantoms to display the utility of high spatial density data and multi-modal information in DOT reconstruction with the two systems

Xanthan gum as an alternative to replace fat for coating and flavoring the extruded snacks

Food industries adapt their products and processes to the needs and desires of consumers. Extruded snacks include 10–20% fat sprinkled to fix flavors, seasonings, and salt. Considering the need to flavor snacks and simultaneously reduce the intake of calories, a polysaccharide is proposed in this study as a fat replacer. Impact of aqueous xanthan gum (Xg) solutions (0.25, 0.5, 1.0%) under two pH conditions (3.5 and 7.0) on structural and sensory characteristics of extruded snacks was analyzed. Rheological features of the coating solutions, as flow behaviour and viscoelastic profile (storage and loss moduli), were assessed. Texture analysis, to evaluate the snacks firmness and moisture content, water activity, retraction, and agglomeration index of the coated snacks, were also evaluated. Results for the aqueous Xg coatings were very encouraging showing good coating properties, not damaging the texture of the extrudates or causing agglomeration. Sensory analysis reflected a good overall acceptability of these snacks, as compared to oil-coated snacks. Therefore, xanthan gum should be used by the industry, to replace fat, on extruded snacks flavor coating solutionsinfo:eu-repo/semantics/publishedVersio

Does a perception of increased blood safety mean increased blood transfusion? An assessment of the risk compensation theory in Canada

BACKGROUND: The risk compensation theory is a widely used concept in transport economics to analyze driver risk behaviour. This article explores the feasibility of applying the theory in blood transfusion to raise important questions regarding the increased blood safety measures and their possible effects on blood usage (e.g., the appropriateness in transfusion). Further, it presents the findings of a pilot survey of physicians in Canada. DISCUSSION: While studies have attempted to define transfusion appropriateness, this article argues that if the risk compensation theory holds true for transfusion practice, physicians may actually be transfusing more. This may increase the possibility of contracting other unknown risks, such as the variant Creutzfeldt-Jakob Disease (vCJD), as well as increasing the risk of non-infectious transfusion risks, such as transfusion reactions. SUMMARY: A much larger study involving psychosocial assessment of physician decision making process to fully assess physician behaviour within the context of risk compensation theory and transfusion practice in Canada is needed to further explore this area

Ectopic A-lattice seams destabilize microtubules

Natural microtubules typically include one A-lattice seam within an otherwise helically symmetric B-lattice tube. It is currently unclear how A-lattice seams influence microtubule dynamic instability. Here we find that including extra A-lattice seams in GMPCPP microtubules, structural analogues of the GTP caps of dynamic microtubules, destabilizes them, enhancing their median shrinkage rate by >20-fold. Dynamic microtubules nucleated by seeds containing extra A-lattice seams have growth rates similar to microtubules nucleated by B-lattice seeds, yet have increased catastrophe frequencies at both ends. Furthermore, binding B-lattice GDP microtubules to a rigor kinesin surface stabilizes them against shrinkage, whereas microtubules with extra A-lattice seams are stabilized only slightly. Our data suggest that introducing extra A-lattice seams into dynamic microtubules destabilizes them by destabilizing their GTP caps. On this basis, we propose that the single A-lattice seam of natural B-lattice MTs may act as a trigger point, and potentially a regulation point, for catastrophe

Enhanced AGAMOUS expression in the centre of the Arabidopsis flower causes ectopic expression over its outer expression boundaries

Spatial regulation of C-function genes controlling reproductive organ identity in the centre of the flower can be achieved by adjusting the level of their expression within the genuine central expression domain in Antirrhinum and Petunia. Loss of this control in mutants is revealed by enhanced C-gene expression in the centre and by lateral expansion of the C-domain. In order to test whether the level of central C-gene expression and hence the principle of ‘regulation by tuning’ also applies to spatial regulation of the C-function gene AGAMOUS (AG) in Arabidopsis, we generated transgenic plants with enhanced central AG expression by using stem cell-specific CLAVATA3 (CLV3) regulatory sequences to drive transcription of the AG cDNA. The youngest terminal flowers on inflorescences of CLV3::AG plants displayed homeotic features in their outer whorls indicating ectopic AG expression. Dependence of the homeotic feature on the age of the plant is attributed to the known overall weakening of repressive mechanisms controlling AG. Monitoring AG with an AG-I::GUS reporter construct suggests ectopic AG expression in CLV3::AG flowers when AG in the inflorescence is still repressed, although in terminating inflorescence meristems, AG expression expands to all tissues. Supported by genetic tests, we conclude that upon enhanced central AG expression, the C-domain laterally expands necessitating tuning of the expression level of C-function genes in the wild type. The tuning mechanism in C-gene regulation in Arabidopsis is discussed as a late security switch that ensures wild-type C-domain control when other repressive mechanism starts to fade and fail

Aspects of the political economy of development and synthetic biology

What implications might synthetic biology’s potential as a wholly new method of production have for the world economy, particularly developing countries? Theories of political economy predict that synthetic biology can shift terms of trade and displace producers in developing countries. Governments, however, retain the ability to mitigate negative changes through social safety nets and to foster adaptation to some changes through research, education and investment. We consider the effects the synthetic production of otherwise naturally derived molecules are likely to have on trade and investment, particularly in developing countries. Both rubber in Malaysia and indigo dyes in India provide historical examples of natural molecules that faced market dislocations from synthetic competitors. Natural rubber was able to maintain significant market share, while natural indigo vanished from world markets. These cases demonstrate the two extremes of the impact synthetic biology might have on naturally derived products. If developing countries can cushion the pain of technological changes by providing producers support as they retool or exit, the harmful effects of synthetic biology can be mitigated while its benefits can still be captured