Probleme bei der Flüssig-flüssig-Extraktion extrazellulärer Produkte direkt aus der Fermenterbrühe

Problems with Liquid Liquid Extraction of Extracellular Products Direct from Fermenter Broths Liquid liquid extraction is usable for separation of extracellular fermentation products. The direct extraction of products from fermenter broths which still contain the cells has important advantages compared to other methods: It shows low losses of products, high product concentrations and low flow rates. The expenditure of equipments is low and it is possible to influence the fermentation in the case of an in situ extraction. These advantages are faced to disadvantages caused by the own properties of fermenter broths. Especially the hydrodynamic behaviour of the two phase system in the extractor is affected by high viscosities and the cells. Further problems are the hindrance of the mass transfer and the selection of suitable solvents for the in situ extraction.     

Interactions between serine acetyltransferase and O-acetylserine (thiol) lyase in higher plants--structural and kinetic properties of the free and bound enzymes

The last steps of cysteine synthesis in plants involve two consecutive enzymes. The first enzyme, serine acetyltransferase, catalyses the acetylation of L-serine in the presence of acetyl-CoA to form O-acetylserine. The second enzyme, O-acetylserine (thiol) lyase, converts O-acetylserine to L-cysteine in the presence of sulfide. We have, in the present work, over-produced in Escherichia coli harboring various type of plasmids, either a plant serine acetyltransferase or this enzyme with a plant O-acetylserine (thiol) lyase. The free recombinant serine acetyltransferase (subunit mass of 34 kDa) exhibited a high propensity to form high-molecular-mass aggregates and was found to be highly unstable in solution. However, these aggregates were prevented in the presence of O-acetylserine (thiol) lyase (subunit mass of 36 kDa). Under these conditions homotetrameric serine acetyltransferase associated with two molecules of homodimeric O-acetylserine (thiol) lyase to form a bienzyme complex (molecular mass approximately 300 kDa) called cysteine synthase containing 4 mol pyridoxal 5'-phosphate/mol complex. O-Acetylserine triggered the dissociation of the bienzyme complex, whereas sulfide counteracted the action of O-acetylserine. Protein-protein interactions within the bienzyme complex strongly modified the kinetic properties of plant serine acetyltransferase: there was a transition from a typical Michaelis-Menten model to a model displaying positive kinetic co-operativity with respect to serine and acetyl-CoA. On the other hand, the formation of the bienzyme complex resulted in a very dramatic decrease in the catalytic efficiency of bound O-acetylserine (thiol) lyase. The latter enzyme behaved as if it were a structural and/or regulatory subunit of serine acetyltransferase. Our results also indicated that bound serine acetyltransferase produces a build-up of O-acetylserine along the reaction path and that the full capacity for cysteine synthesis can only be achieved in the presence of a large excess of free O-acetylserine (thiol) lyase. These findings contradict the widely held belief that such a bienzyme complex is required to channel the metabolite intermediate O-acetylserine.     

Mycobacterium leprae binds to a 25-kDa phosphorylated glycoprotein of human peripheral nerve

Mycobacterium leprae, the causative agent of leprosy, specifically invades and destroys the peripheral nerve, which results in the main clinical manifestation of the disease. Little is known about the bacteria-nerve protein interaction. We show in the present work that M leprae binds to a 25 kDa glycoprotein from human peripheral nerve. This protein is phosphorylatable and it binds to lectins which have alpha-mannose specificity. This M leprae-protein interaction could be of importance in the pathogenesis of leprosy.     

The effect of grammatical gender on object categorization.

In 3 experiments, we investigated the effect of grammatical gender on object categorization. Participants were asked to judge whether 2 objects, whose names did or did not share grammatical gender, belonged to the same semantic category by pressing a key. Monolingual speakers of English (Experiment 1), Italian (Experiments 1 and 2), and Spanish (Experiments 2 and 3) were tested in their native language. Italian and Spanish participants responded faster to pairs of stimuli sharing the same gender, whereas no difference was observed for English participants. In Experiment 2, the pictures were chosen in such a way that the grammatical gender of the names was opposite in Italian and Spanish. Therefore, the same pair of stimuli gave rise to different patterns depending on the gender congruency of the names in the languages. In Experiment 3, Spanish speakers performed the same task under an articulatory suppression condition, showing no grammatical gender effect. The locus where meaning and gender interact can be located at the level of the lexical representation that specifies syntactic information: Nouns sharing the same grammatical gender activate each other, thus facilitating their processing and speeding up responses, either to semantically related pairs or to semantically unrelated pairs. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Solving the infinite-dimensional discrete-time algebraic riccati equation using the extended symplectic pencil

In this paper we present results about the algebraic Riccati equation (ARE) and a weaker version of the ARE, the algebraic Riccati system (ARS), for infinite-dimensional, discrete-time systems. We introduce an operator pencil, associated with these equations, the so-called extended symplectic pencil (ESP). We present a general form for all linear bounded solutions of the ARS in terms of the deflating subspaces of the ESP. This relation is analogous to the results of the Hamiltonian approach for the continuous-time ARE and to the symplectic pencil approach for the finite-dimensional discrete-time ARE. In particular, we show that there is a one-to-one relation between deflating subspaces with a special structure and the solutions of the ARS. Using the relation between the solutions of the ARS and the deflating subspaces of the ESP, we give characterizations of self-adjoint, nonnegative, and stabilizing solutions. In addition we give criteria for the discrete-time, infinite-dimensional ARE to have a maximal self-adjoint solution. Furthermore, we consider under which conditions a solution of the ARS satisfies the ARE as well.     

Influence of the carbon texture of platinum/carbon aerogel electrocatalysts on their behavior in a proton exchange membrane fuel cell cathode

Seven carbon aerogels (CAs) with different pore size distributions were synthesized and used as a catalyst support in proton exchange membrane fuel cell (PEMFC) cathodes. The cathodes were tested in 50 cm² membrane electrode assemblies. The results demonstrate that the CA texture significantly influences performance by impacting gas diffusion and proton transport. Also, the Nafion^® loading must be adapted to the CA texture, since its easier penetration into large pores favors their obstruction and results in higher proton resistance and mass-transport voltage losses. Under fixed experimental conditions (notably Nafion^®/carbon ratio = 1), the best CA support displays high specific surface area and pore volume, a majority of mesopores with a pore size distribution peak around 25–30 nm and with some macropores. The work confirms that the carbon support structure must be controlled to reduce mass-transport voltage losses. Doing so would lead to reduce PEMFC overall cost per kW.