The many-body linear response expressions obtained in previous papers [J. Math. Phys. 19, 1345 (1978); 20, 2573 (1979)] are applied to systems of weakly interacting particles. General expressions for the susceptibility and conductivity in such systems are obtained. The diagonal parts depend on the scattering processes, for which we consider interactions with bosons with mass and electron-phonon interaction. For elastic collisions simple closed forms result. For general two-body collisions, the closed expressions are cumbersome, except when the current is due to collisional current through localized states, such as Landau orbits; in that event a generalized Adams-Holstein result is obtained. The nondiagonal electrical conductivity is shown to be of paramount importance for the quantum mechanical Hall effect. We also derive quantum mechanical Boltzmann equations, both for the diagonal occupancy operator 〈nζ〉t and for the nondiagonal operator 〈c+ζ′ cζ\〉t. The total Boltzmann equation is shown to be fully equivalent with the linear response results. Finally, in the last part we derive the Boltzmann equation for the Wigner function of inhomogeneous systems. In the classical limit this yields the usual Boltzmann transport equation. This equation has therefore been obtained by first principles from the von Neumann equation.

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The first relaxed excited state energy of the free Frohlich polaron is evaluated using the Fock approximation of Matz and Burkey. From a discussion of a variational-type expression of this energy, it is concluded that a singularity in the space of variational parameters separates the ground state from the first relaxed excited state and that other singularities separate the other excited states. From this interpretation, this energy is evaluated, using two complete model spectra; a Gaussian spectrum and a second one involving an internal magnetic field in addition to the Gaussian part. It is found that for a 5 1.2 no excited state is observed. For 1.2 a 5 4.2, a two-dimensional excited state is obtained while for a 2 4.2 aGaussian excited state is obtained.These results are, however,limited by the choice of the model spectrum. For large a's, an asymptotic limit is obtained of -0.053a2hw, a value close to that obtained from the best product ansatz calculations.Nous evaluons 1'6nergie du premier Atat excite relachk du polaron libre de Frohlich, en utilisant l'approximation de Fock de Matz et Burkey. D'une discussion d'une expression de type variationnel de cette energie, nous concluons qu'une singularite dans l'espace des parametres &pare 1'6tat fondamental du premier &tat excite relache et que d'autres singularites &parent les autres Btats excites. A l'aide de cette interpretation, nous evaluons cette Bnergie, avec deux spectres modeles complets: le spectre Gaussien et un spectre impliquant un champ magnetique interne en plus de la partie Gaussienne. Nous trouvons que pour a 5 1,2, il n'existe aucun &at excite. Pour 1,2 4,2, un Btat excite bi-dimensionnel est obtenu tandis que pour a 2 4,2, un &at excite Gaussien est obtenu. Ces resultats sont cependant limites par le choix du spectre modAle. Pour de grandes valeurs de a, nous obtenons une limite asymptotique de -0,053a2hw, une valeur proche de celles obtenues des meilleurs calculs de la methode du produit ansatz. a

The cleavage of the autotransporter adhesin involved in diffuse adherence (AIDA-I) of Escherichia coli yields a membraneembedded fragment, AIDAc, and an extracellular fragment, the mature AIDA-I adhesin. The latter remains noncovalently associated with AIDAc but can be released by heat treatment. In this study we determined the mechanism of AIDA-I cleavage. We showed that AIDA-I processing is an autocatalytic event by monitoring the in vitro cleavage of an uncleaved mutant protein isolated from inclusion bodies. Furthermore, by following changes in circular dichroism spectra and protease resistance of the renaturated protein, we showed that the cleavage of the protein is correlated with folding. With site-directed deletions, we showed that the catalytic activity of the protein lies in a region encompassing amino acids between Ala-667 and Thr-953, which includes the conserved junction domain of some autotransporters. With site-directed point mutations, we also found that Asp-878 and Glu-897 are involved in the processing of AIDA-I and that a mutation preserving the acidic side chain of Asp-878 was tolerated, giving evidence that this carboxylic acid group is directly involved in catalysis. Last, we confirmed that cleavage of AIDA-I is intramolecular. Our results unveil a new mechanism of auto-processing in the autotransporter family.Monomeric autotransporters, secreted by the type Va secretion pathway, constitute one of the largest family of secreted proteins in Gram-negative bacteria (1). Various virulence attributes have been associated with most autotransporters, such as adhesion or invasion, self-association, biofilm formation, serum resistance, and cytotoxic activity to name just a few (2, 3). Autotransporters are synthesized as pre-proproteins with modular organizations. An N-terminal sec-dependent signal sequence permits the secretion of the protein across the inner membrane (4). A C-terminal membrane-embedded domain promotes secretion of parts of the protein across the outer membrane and is composed of a ␤-barrel and a ␣-helix spanning its lumen (5, 6). The central domain of the protein is, thus, extracellular and bears its functional part. In some cases the extracellular part of the protein is cleaved and remains associated with the outer membrane or is secreted in the extracellular milieu. Directly preceding the membrane-embedded domain, a functional subdomain of ϳ100 amino acids is sometimes present in the extracellular domain and has been called the junction region (also named autochaperone domain or stable core) (7-9). This region is essential for stabilizing the ␤-barrel and/or to promote folding of the extracellular domain (7-9).The adhesin involved in diffuse adherence (AIDA-I) 3 is a monomeric autotransporter that has been extensively studied. AIDA-I was originally identified as a plasmid-encoded protein from a diffusely adhering Escherichia coli strain isolated in a case of infantile diarrhea (10). This adhesin was then shown to play a role in neonatal and postweaning diarrheal diseases in pigle...

SUMMARY:Leucocyte Glutamate Dehydrogenase (GDH) activity was measured in 44 patients with various forms of ataxia and 44 age and sex-matched normal controls. The only significant change found was a moderate decrease in activity in Freidreich's ataxia and a few patients with OPCA. This decreased activity is not primary to the disease but probably reflects a regulatory defect affecting mitochondrial membranes in these patients.