[Brain localization of semantic processing]. / Localizacion cerebral del procesamiento semantico.

INTRODUCTION: Semantic content processing is associated with the potential N400, and the P600 is linked with the processing of syntactic and grammatical rules. AIM: To verify whether the semantic processing of complex visual stimuli such as repetition, identity, order and double incongruence is recursive or computable. SUBJECTS AND METHODS: 27 university students responded to an adapted N400 paradigm with five conditions, each with 80 tasks, while recording their brain activity with a 64-channel cap. RESULTS: Two temporal windows of 400 to 550 ms and 550 to 800 ms were analyzed using an ANOVA contrast of the condition factor by regions of interest. In addition, the inverse solution of the windows was calculated by low resolution electromagnetic tomography (LORETA) to identify the main sources related to the electrical power. The significant differences (p <0.05) in the results for the N400 and P600 in frontal and centroparietal areas in the logical operators studied are corroborated. CONCLUSION: It is confirmed that the brain processing of complex images is modulated by repetition, identity and order, but not by negation. Therefore, it can be said that the semantic processing of complex images is semi-computable.

TITLE: Localizacion cerebral del procesamiento semantico.Introduccion. El procesamiento del contenido semantico se asocia al potencial N400, y el P600 se vincula con el procesamiento de reglas sintacticas y gramaticales. Objetivo. Verificar si el procesamiento semantico de estimulos visuales complejos, como la repeticion, la identidad, el orden y la doble incongruencia, es recursivo o computable. Sujetos y metodos. Veintisiete universitarios respondieron a un paradigma adaptado N400 con cinco condiciones, cada una con 80 tareas, mientras se registraba su actividad cerebral con un gorro de 64 electrodos. Resultados. Dos ventanas temporales de 400 a 550 ms y de 550 a 800 ms se analizaron mediante un contraste ANOVA del factor condicion por regiones de interes. Ademas, se calculo la solucion inversa de las ventanas mediante tomografia electromagnetica de baja resolucion para identificar las fuentes corticales subyacentes a los potenciales electricos. Se corroboran diferencias significativas (p < 0,05) en los potenciales N400 y P600 en areas frontales y centroparietales asociadas a los operadores logicos estudiados. Conclusion. Se confirma que el procesamiento cerebral de imagenes complejas (congruentes/incongruentes) es modulado por la repeticion, la identidad y el orden, pero no por la negacion. Por consiguiente, se puede decir que el procesamiento semantico de imagenes complejas es semicomputable.

Evidence Linking Brain Activity Modulation to Age and to Deductive Training.

Electrical brain activity modulation in terms of changes in its intensity and spatial distribution is a function of age and task demand. However, the dynamics of brain modulation is unknown when it depends on external factors such as training. The aim of this research is to verify the effect of deductive reasoning training on the modulation in the brain activity of healthy younger and older adults (N = 47 (mean age of 21 ± 3.39) and N = 38 (mean age of 68.92 ± 5.72)). The analysis reveals the benefits of training, showing that it lowers cerebral activation while increasing the number of correct responses in the trained reasoning task (p < 0.001). The brain source generators were identified by time-averaging low-resolution brain electromagnetic tomography (sLORETA) current density images. In both groups, a bilateral overactivation associated with the task and not with age was identified. However, while the profile of bilateral activation in younger adults was symmetrical in anterior areas, in the older ones, the profile was located asymmetrically in anterior and posterior areas. Consequently, bilaterality may be a marker of how the brain adapts to maintain cognitive function in demanding tasks in both age groups. However, the differential bilateral locations across age groups indicate that the tendency to brain modulation is determined by age.

Selective adsorption of poly-His tagged glutaryl acylase on tailor-made metal chelate supports.

A poly-His tag was fused in the glutaryl acylase (GA) from Acinetobacter sp. strain YS114 cloned in E. coli yielding a fully active enzyme. Biochemical analyses showed that the tag did not alter the maturation of the chimeric GA (poly-His GA) that undergoes a complex post-translational processing from an inactive monomeric precursor to the active heterodimeric enzyme. This enzyme has been used as a model to develop a novel and very simple procedure for one-step purification of poly-His proteins via immobilized metal-ion affinity chromatography on tailor-made supports. It was intended to improve the selectivity of adsorption of the target protein on tailor-made chelate supports instead of performing a selective desorption. The rate and extent of the adsorption of proteins from a crude extract from E. coli and of pure poly-His tagged GA on different metal chelate supports was studied. Up to 90% of proteins from E. coli were adsorbed on commercial chelate supports having a high density of ligands attached to the support through long spacer arms, while this adsorption becomes almost negligible when using low ligand densities, short spacer arms and Zn2+ or Co2+ as cations. On the contrary, poly-His GA adsorbs strongly enough on all supports. A strong affinity interaction between the poly-His tail and a single chelate moiety seems to be the responsible for the adsorption of poly-His GA. By contrast, multipoint weak interactions involving a number of chelate moieties seem to be mainly responsible for adsorption of natural proteins. By using tailor-made affinity supports, a very simple procedure for one-step purification of GA with minimal adsorption of host proteins could be performed. Up to 20 mg of GA were adsorbed on each ml of chelate support while most of accompanying proteins were hardly adsorbed on such supports. Following few washing steps, the target enzyme was finally recovered (80% yield) by elution with 50 mM imidazole with a very high increment of specific activity (up to a 120 purification factor).

Molecular cloning and expression in different microbes of the DNA encoding Pseudomonas putida U phenylacetyl-CoA ligase. Use of this gene to improve the rate of benzylpenicillin biosynthesis in Penicillium chrysogenum.

The gene encoding phenylacetyl-CoA ligase (pcl), the first enzyme of the pathway involved in the aerobic catabolism of phenylacetic acid in Pseudomonas putida U, has been cloned, sequenced, and expressed in two different microbes. In both, the primary structure of the protein was studied, and after genetic manipulation, different recombinant proteins were analyzed. The pcl gene, which was isolated from P. putida U by mutagenesis with the transposon Tn5, encodes a 48-kDa protein corresponding to the phenylacetyl-CoA ligase previously purified by us (Martínez-Blanco, H., Reglero, A. Rodríguez-Aparicio, L. B., and Luengo, J. M. (1990) J. Biol. Chem. 265, 7084-7090). Expression of the pcl gene in Escherichia coli leads to the appearance of this enzymatic activity, and cloning and expression of a 10.5-kb DNA fragment containing this gene confer this bacterium with the ability to grow in chemically defined medium containing phenylacetic acid as the sole carbon source. The appearance of phenylacetyl-CoA ligase activity in all of the strains of the fungus Penicillium chrysogenum transformed with a construction bearing this gene was directly related to a significant increase in the quantities of benzylpenicillin accumulated in the broths (between 1.8- and 2.2-fold higher), indicating that expression of this bacterial gene (pcl) helps to increase the pool of a direct biosynthetic precursor, phenylacetyl-CoA. This report describes the sequence of a phenylacetyl-CoA ligase for the first time and provides direct evidence that the expression in P. chrysogenum of a heterologous protein (involved in the catabolism of a penicillin precursor) is a useful strategy for improving the biosynthetic machinery of this fungus.

Changing the substrate specificity of penicillin G acylase from Kluyvera citrophila through selective pressure.

Escherichia coli (muT, mutD, Leu-) cells transformed with plasmid pYKD59 harbouring the pac gene encoding penicillin acylase (PA) from Kluyvera citrophila ATCC 21285 were exposed to environmental conditions that made expression of this enzyme essential for growth. Under these conditions, spontaneous mutants were isolated that used adipyl-L-leucine as the sole source of L-leucine. DNA sequencing of the mutant pac genes identified a transversion mutation of thymine to guanine at position 1163. This mutation was located in the beta-subunit of the enzyme and resulted in conversion of Phe-360 to valine. The assignment of this mutation to the shift in substrate specificity was further confirmed by site-directed mutagenesis. Secondary-structure prediction of the region surrounding Phe-360 suggests that this mutation should not produce any significant structural change. The purified mutant acylase was able to hydrolyse adipyl-, glutaryl-, valeryl-, caproyl-, heptanoyl- and phenoxyacetyl-L-leucine at pH 5 with greater efficiency than the wild-type enzyme. However, the mutant enzyme was not able to hydrolyse glutaryl-7-aminocephalosporanic acid and had lost 90% and 50% of activity on penicillin G and phenylacetyl-L-leucine respectively. Nevertheless, mutant PA retained its original activity on 6-nitro-3-phenylacetamidobenzoate and p-nitrophenylphenylacetate, suggesting that the binding specificity of PA by the acyl and amine moieties of the substrate are not independent phenomena. The small differences observed between the c.d. spectra of the mutant enzyme recorded at pH 5 and 8 suggest the existence of different conformational states at the two pH values, but these differences were indistinguishable from those observed in the native enzyme and cannot be correlated with the shift in substrate specificity. Our results demonstrate that it is possible to change the specificity of PA by laboratory evolution and use it to identify the amino acids involved in substrate recognition. However, the synchronous participation of the alpha- and beta-subunits in the complex induced-fit-like mechanism of acylases suggests that, to obtain new enzymes for industrial application, the selection pressure should be specifically designed for the compound of interest.

The comparative stability of different types of penicillin and cephalosporin N-pyrryl derivatives.

The kinetics of the decomposition of potassium salts of 4-thia-1-azabicyclo[3.2.0.]heptane-3,3-dimethyl-6-amino-7-oxo-N- [2(1H-pyrrolyl)acetyl] -2-carboxylic acid (6R, trans), 4-thia-1-azabicyclo[3.2.0]heptane-3,3-dimethyl-6-amino-7-oxo-N-[2-phenyl - 2(1H-pyrrolyl)acetyl]-2-carboxylic acid (6R, trans), 5-thia-1-azabicyclo[4.2.0.]oct-2-ene-3- [(acetyloxy)methyl]-7-amino-8-oxo-N-[2(1H-pyrrolyl)acetyl]-2-ca rbo xylic acid (6R, trans), 5-thia-1-azabicyclo[4.2.0.]oct-2-ene-3- [(acetyloxy)methyl]-7-amino-8-oxo-N-[2-phenyl-2(1H-pyrrolyl)acetyl ]- 2-carboxylic acid (6R, trans), 5-thia-1-azabicyclo[4.2.0.]oct-2-ene-7-amino-3-methyl-8-oxo-N- [2(1H-pyrrolyl)-acetyl]-2-carboxylic acid (6R, trans) and 5-thia-1-azabicyclo[4.2.0.]oct-2-ene-7-amino-3-methyl-8-oxo- N-[2-phenyl-2(1H-pyrrolyl)acetyl]-2-carboxylic acid (6R, trans), in aqueous solution at 37 degrees C and at ionic strength of 0.5 mol.l-1 have been studied over the 2.3-11.5 pH range. In all cases, the hydrolysis of these compounds is subject to acid-base catalysis and, in some instances, to a general catalysis by various species present in the buffer solutions. The experimental results have been analyzed and discussed in relation to the hydrolytic mechanisms.

Cyclization of phenylacetyl-L-cysteinyl-D-valine to benzylpenicillin using cell-free extracts of Streptomyces clavuligerus.

Benzylpenicillin, a typical antibiotic produced by some species of fungi, was obtained by direct cyclization of the heteropeptide phenylacetyl-L-cysteinyl-D-valine using cell-free extracts of Streptomyces clavuligerus. This is the first description of evidence of the synthesis of benzylpenicillin from a non natural molecule using a bacterial enzyme.

Interactions of cephalosporins and penicillins with nonpolar macroporous styrenedivinylbenzene copolymers.

The conditions of sorption of penicillins and cephalosporins on nonionic macroporous copolymers of styrenedivinylbenzene were evaluated. By increasing the methanol concentration in the eluent, the sorption decreased. Salts exerted little influence on sorption. However, pH exerted a remarkable effect on sorption, and the capacity factor variations according to the pH are quantitatively described. Some typical separations are shown.

Interactions of cephalosporins and penicillins with nonpolar octadecylsilyl stationary phase.

The capacity factors of several penicillins and cephalosporins, as well as those of 7-aminocephalosporanic acid, 6-aminopenicillanic acid, and 7-aminodeacetoxycephalosporanic acid, were determined at pH 2.5-7.5 with different methanol concentrations in the mobile phase. The influence of ionic strength on activity factors also was studied. Some theoretical equations providing a quantitative description of the influence of the mobile phase pH on the retention of penicillins and cephalosporins by an octadecylsilyl stationary phase were established. The analysis of experimental data by a nonlinear least-squares fit to theoretically deduced equations permitted determination of the capacity factors of anionic, cationic, zwitterion, and undissociated forms of the substances studied.