Neural correlates of the difference between working memory speed and simple sensorimotor speed: an fMRI study

The difference between the speed of simple cognitive processes and the speed of complex cognitive processes has various psychological correlates. However, the neural correlates of this difference have not yet been investigated. In this study, we focused on working memory (WM) for typical complex cognitive processes. Functional magnetic resonance imaging data were acquired during the performance of an N-back task, which is a measure of WM for typical complex cognitive processes. In our N-back task, task speed and memory load were varied to identify the neural correlates responsible for the difference between the speed of simple cognitive processes (estimated from the 0-back task) and the speed of WM. Our findings showed that this difference was characterized by the increased activation in the right dorsolateral prefrontal cortex (DLPFC) and the increased functional interaction between the right DLPFC and right superior parietal lobe. Furthermore, the local gray matter volume of the right DLPFC was correlated with participants' accuracy during fast WM tasks, which in turn correlated with a psychometric measure of participants' intelligence. Our findings indicate that the right DLPFC and its related network are responsible for the execution of the fast cognitive processes involved in WM. Identified neural bases may underlie the psychometric differences between the speed with which subjects perform simple cognitive tasks and the speed with which subjects perform more complex cognitive tasks, and explain the previous traditional psychological findings.     

Mammalian Atg2 proteins are essential for autophagosome formation and important for regulation of size and distribution of lipid droplets

Macroautophagy is an intracellular degradation system by which cytoplasmic materials are enclosed by the autophagosome and delivered to the lysosome. Autophagosome formation is considered to take place on the endoplasmic reticulum and involves functions of autophagy-related (Atg) proteins. Here, we report the identification and characterization of mammalian Atg2 homologues Atg2A and Atg2B. Simultaneous silencing of Atg2A and Atg2B causes a block in autophagic flux and accumulation of unclosed autophagic structures containing most Atg proteins. Atg2A localizes on the autophagic membrane, as well as on the surface of lipid droplets. The Atg2A region containing amino acids 1723-1829, which shows relatively high conservation among species, is required for localization to both the autophagic membrane and lipid droplet and is also essential for autophagy. Depletion of both Atg2A and Atg2B causes clustering of enlarged lipid droplets in an autophagy-independent manner. These data suggest that mammalian Atg2 proteins function both in autophagosome formation and regulation of lipid droplet morphology and dispersion.     

Sequence Analysis of Amplified DNA Fragments Containing the Region Encoding the Putative Lipase Substrate-Binding Domain and Genotyping of Aeromonas hydrophila

DNA fragments were amplified by PCR from all tested strains of Aeromonas hydrophila, A. caviae, and A. sobria with primers designed based on sequence alignment of all lipase, phospholipase C, and phospholipase A1 genes and the cytotonic enterotoxin gene, all of which have been reported to have the consensus region of the putative lipase substrate-binding domain. All strains showed lipase activity, and all amplified DNA fragments contained a nucleotide sequence corresponding to the substrate-binding domain. Thirty-five distinct nucleotide sequence patterns and 15 distinct deduced amino acid sequence patterns were found in the amplified DNA fragments from 59 A. hydrophila strains. The deduced amino acid sequences of the amplified DNA fragments from A. caviae and A. sobria strains had distinctive amino acids, suggesting a species-specific sequence in each organism. Furthermore, the amino acid sequence patterns appear to differ between clinical and environmental isolates among A. hydrophila strains. Some strains whose nucleotide sequences were identical to one another in the amplified region showed an identical DNA fingerprinting pattern by repetitive extragenic palindromic sequence-PCR genotyping. These results suggest that A. hydrophila, and also A. caviae and A. sobria strains, have a gene encoding a protein with lipase activity. Homologs of the gene appear to be widely distributed in Aeromonas strains, probably associating with the evolutionary genetic difference between clinical and environmental isolates of A. hydrophila. Additionally, the distinctive nucleotide sequences of the genes could be attributed to the genotype of each strain, suggesting that their analysis may be helpful in elucidating the genetic heterogeneity of Aeromonas.     

Further insight into the mechanism of stereoselective proton abstraction by bacterial copper amine oxidase

During the catalytic reaction of copper amine oxidase, one of the two prochiral hydrogen atoms at the C1 position of substrate amine is stereoselectively abstracted by a conserved Asp residue serving as a general base. Using stereospecifically deuterium-labeled enantiomers of 2-phenylethylamine, we previously showed that the pro-S alpha-proton is abstracted by the enzyme from Arthrobacter globiformis (AGAO) [Uchida, M., et al. (2003) Biosci. Biotechnol. Biochem. 67, 2664-2667]. More recently, we have also demonstrated that the pro-S selectivity of alpha-proton abstraction is fully retained even in the reaction of a mutant AGAO lacking the catalytic base [Chiu, Y.-C., et al. (2006) Biochemistry 45, 4105-4120]. On the basis of these findings, we have proposed that the stereoselectivity of alpha-proton abstraction is primarily determined by the conformation of the Schiff base intermediate formed between the substrate and the topa quinone cofactor (TPQ), stabilized by the binding of the distal part of the substrate to a hydrophobic pocket of the enzyme. In this conformation, the pro-S hydrogen atom to be abstracted is nearly perpendicular to the plane of the Schiff base-TPQ conjugate system, achieving the maximum overlap of sigma- and pi-orbitals. To further elucidate the stereochemical details, we have synthesized stereospecifically deuterium-labeled enantiomers of ethylamine, a very poor substrate for AGAO, in addition to those structurally related to the preferred substrate, 2-phenylethylamine. In marked contrast to the nearly complete pro-S selectivity of alpha-proton abstraction for most substrates that have been examined, the stereoselectivity for ethylamine decreased significantly to as little as 88%. The crystal structure of AGAO soaked with ethylamine showed very poor electron densities for the substrate Schiff base intermediate, showing that its conformation is not defined uniquely. Thus, the stereoselectivity of alpha-proton abstraction during the copper amine oxidase reaction is closely associated with the conformational flexibility of the substrate Schiff base intermediate.     

Effect of butyrate on glycolipid metabolism of two cell types of rat ascites hepatomas with different ganglioside biosynthesis

The effect of butyrate on glycolipid metabolism and morphological differentiation in the cell culture system of rat ascites hepatomas, AH 7974 of island-forming type and AH 7974F of free type, was studied. Both cell lines adhered to the substratum in the presence of 1 mM butyrate. In the case of AH 7974, the addition of butyrate induced a distinct morphological change but the other cell line showed no such conspicuous change. Butyrate-treated AH 7974 cells showed a 2 to 3-fold elevation of CMP-N-acetylneuraminic acid: lactosylceramide sialyltransferase activity to form N-acetylneuraminylgalactosylglucosylceramide (GM3). On the other hand, no enzyme activity could be detected in AH 7974F cells. Four glycosyltransferase activities involved in glycolipid synthesis, including sialyltransferase in AH 7974F cells, were reduced by butyrate. From these observations we concluded that sialyltransferase to form GM3, or TM3 itself, is prerequisite for the morphological alteration induced by butyrate.     

Remediation of Gulf War Oil Spill Contaminated Soil by a Subcritical Water Extraction Process: Oil Removal,Recovery, and Degradation

Due to the unique properties of subcritical water (marked change in water's dielectric constant and viscosity), the extraction by subcritical water offers a great opportunity to remediate soil contaminated with organic pollutants as an alternative and green remediation method. In this study, subcritical water extraction is proposed as an efficient remediation technique for the Gulf War oil spill contaminated soil. The subcritical water extraction experiment was carried out in a lab-scale continuous flow apparatus. The three major operating factors, temperature, time and water flow rate, were evaluated in terms of optimum removal efficiency. The results show that crude oil removal depended largely on water temperature, whereas an extraction run time higher than 1 h and a water flow rate higher than 1.5 mL/min marginally or negatively affected removal efficiency. During subcritical water treatment at 300°C for 1 h at a flow rate of 1.5 mL/min, removal efficiency was almost 95%. Under these operating conditions, the subcritical water treatment demonstrated a similar removal efficiency to those of organic solvents like acetone. In contrast, the efficiency of oil recovery decreased with an increase in extraction temperature, due to degradation by a water self-oxidizing agent. Several degradation products identified in the treated soil and in the effluent sample (which initially were absent in the contaminated soil) were oxygen-containing aromatic compounds, confirming the oxidation-degradation.