A simple model of human foveal ganglion cell responses to hyperacuity stimuli

We developed a physiologically plausible model of the first steps of spatial visual information processing in the fovea of the human retina. With the predictions of this model we could support the hypothesis that, for moderate contrasts ( 40%), hyperacuity is mediated by the magnocellular (MC-) pathway. Despite the lower sampling density in the MC pathway, as compared to the parvocellular (PC-) pathway, the information that is transferred by the MC ganglion cells is sufficient to achieve thresholds comparable to those of human subjects in psychophysical tasks. This is a result of the much higher signal-to-noise ratio of the MC pathway cell signals. The PC pathway cells do not transfer enough information for hyperacuity thresholds.     

Production of cyclodextrins using moderately heat-treated cornstarch

Cyclodextrins are very useful compounds for the food, cosmetic, pharmaceutic, and plastic industries. We developed a process for the production of cyclodextrins from moderately heat-treated cornstarch. This method had many merits. First, the cyclodextrins were not degraded by cyclodextrin glucanotransferase, because low molecular weight maltodextrins were hardly produced. Second, it was possible to remove the residual cornstarch by a simple method such as filtration or centrifugation. Third, the amount of cyclodextrin glucanotransferase used for cyclodextrin production was less than that using the traditional method. Fourth, the pretreating method was simple. And fifth, the residual starch could be used as substrate for the production of other compounds. Cyclodextrins were produced at optimum conditions: heating temperature was 65°C; heating time was 1 h; concentration of substrate was 7.5%; amount of enzyme loaded was 48 U g⁻¹ of substrate. Using these conditions, the results were as follows: the content of cyclodextrins, 50%; the conversion yield of substrate, 25%; the productivity per enzyme unit, 5.22 mg of cyclodextrins.     

Cloning,characterization and overproduction of nuclease S1 gene (nucS) from Aspergillus oryzae

The nuclease S1 gene (nucS) from Aspergillus oryzae was isolated using a polymerase-chain-reaction-amplified DNA fragment as a probe, and a 2.6-kb SalI-EcoRI fragment containing the nucS gene was sequenced. It was deduced that the nucS gene had two short introns, 49 and 50 nucleotides in lenght. The nucS gene had an open-reading frame of 963 base pairs and coded for a protein of 287 amino acid residues, comprising the signal peptide of 20 amino acids and a mature protein of 267 amino acids. The deduced amino acid sequence agreed well with the published amino acid sequence except for one substitution. Southern hybridization analysis showed that the nucS gene existed as a single copy in the A. oryzae chromosome. When the structural gene of nucS was fused with the promoter of the glaA gene and introduced into A. oryzae, the yield od secreted nuclease S1 increased about 100-fold compared with the recipient strain.     

Methodology in the study of seabass (Lates calcarifer Bloch): nutritional requirements in Singapore

This paper describes the effort of the Marine Aquaculture Section of the Primary Production Department in Singapore and the Institut Francais de Recherche pour l'Exploitation de la Mer in developing adequate facilities for fish nutritional requirement studies in Singapore, and in introducing appropriate nutritional methodology so that results are reliable and accurate. One of the first achievements was the demonstration of homogeneous fish (tropical seabass, Lates calcarifer Bloch) growth response in a newly established tank system before any nutritional experiments were initiated. The application of statistical procedures that take into consideration the power of a test and number of replications required has allowed for more accurate interpretation of results. This can be seen in the results of the first nutritional requirement experiment on the optimal dietary protein level of the seabass at constant energy.     

Evaluation of cellulase recycling strategies for the hydrolysis of lignocellulosic substrates

Recycling of cellulases should lower the overall cost of lignocellulosiic bioconversion processes. In this study, three recycling strategies were evaluated to determine their efficiencies over five successive rounds of hydrolysis. The effect of lignin on recycling was examined by comparing water-washed, steam-exploded birch (WB; 32% lignin) and WB which had been further extracted with alkali and peroxide (PB; 4% lignin). When the cellulases were recovered from the residual substrates after partial hydrolysis of both substrates, the recovered cellulase activity toward the mixture of fresh and residual substrates decreased after each recycling step. When the cellulases in the supernatants were also recycled, up to 20% more activity could be recovered. In both of these cases, the recovered activities did not correspond to the activities expected from the amount of cellulase protein recovered during recycling. The best recovery was obtained when the cellulases were recovered from both the residue and the supernatant after complete hydrolysis of the PB substrate. In this case, all of the originally added cellulase activity could be recovered for four consecutive hydrolysis rounds. However, when the same recycling strategy was carried out using the WB substrate, the recovered cellulase activity declined quickly with each recycling round. In all three of the recycling strategies, lower cellulase activities were recovered from the substrates with higher lignin contents. (c) 1995 John Wiley & Sons, Inc.     

Antitumor agents-CLXXV. Anti-tubulin action of (+)-thiocolchicine prepared by partial synthesis

(+)-Thiocolchicine (2b) was prepared from (±)-colchicine (1) in a five-step reaction sequence that included chromatographic separation of appropriate camphanylated diastereomers. Acid hydrolysis of the (+)-diastereomer, followed by acetylation, yielded the desired product 2b. (+)-Thiocolchicine has 15-fold lower inhibitory activity against tubulin polymerization than (−)-thiocolchicine, and is 29-fold less potent for inhibiting growth of human Burkitt lymphoma cells. The enantiomer 2a, prepared from the (−)-camphanylated diastereomer, had potent activity in all assays comparable to that of (−)-thiocolchicine prepared by other methods. These results support the hypothesis that the proper configuration of colchicine-related compounds is an important requirement for their anti-tubulin action.     

Synthesis and antiplatelet, antiinflammatory, and antiallergic activities of 2-substituted 3-chloro-1,4-naphthoquinone derivatives

A series of 2-substituted 3-chloro-1,4-naphthoquinones was synthesized, and the antiplatelet, antiinflammatory, and antiallergic activities of these compounds were evaluated. The structure-activity relationships in this series were also examined. Most of the 2-alkyl/arylcarboxamido derivatives of 3-chloro-1,4-naphthoquinone showed potent activities with similar trends in each of the activities evaluated.     

Novel β-Secretase Cleavage of β-Amyloid Precursor Protein in the Endoplasmic Reticulum/Intermediate Compartment of NT2N Cells

Previous studies have demonstrated that NT2N neurons derived from a human embryonal carcinoma cell line (NT2) constitutively process the endogenous wild-type β-amyloid precursor protein (APP) to amyloid β peptide in an intracellular compartment. These studies indicate that other proteolytic fragments generated by intracellular processing must also be present in these cells. Here we show that the NH₂-terminal fragment of APP generated by β-secretase cleavage (APPβ) is indeed produced from the endogenous full length APP (APP_FL). Pulse–chase studies demonstrated a precursor–product relationship between APP_FL and APPβ as well as intracellular and secreted APPβ fragments. In addition, trypsin digestion of intact NT2N cells at 4°C did not abolish APPβ recovered from the cell lysates. Furthermore, the production of intracellular APPβ from wild-type APP appears to be a unique characteristic of postmitotic neurons, since intracellular APPβ was not detected in several non-neuronal cell lines. Significantly, production of APPβ occurred even when APP was retained in the ER/ intermediate compartment by inhibition with brefeldin A, incubation at 15°C, or by expression of exogenous APP bearing the dilysine ER retrieval motif.     

Linkage Analysis with Multiplexed Short Tandem Repeat Polymorphisms Using Infrared Fluorescence and M13 Tailed Primers

The use of short tandem repeat polymorphisms (STRPs) as marker loci for linkage analysis is becoming increasingly important due to their large numbers in the human genome and their high degree of polymorphism. Fluorescence-based detection of the STRP pattern with an automated DNA sequencer has improved the efficiency of this technique by eliminating the need for radioactivity and producing a digitized autoradiogram-like image that can be used for computer analysis. In an effort to simplify the procedure and to reduce the cost of fluorescence STRP analysis, we have developed a technique known as multiplexing STRPs with tailed primers (MSTP) using primers that have a 19-bp extension, identical to the sequence of an M13 sequencing primer, on the 5′ end of the forward primer in conjunction with multiplexing several primer pairs in a single polymerase chain reaction (PCR) amplification. The banding pattern is detected with the addition of the M13 primer-dye conjugate as the sole primer conjugated to the fluorescent dye, eliminating the need for direct conjugation of the infrared fluorescent dye tn the STRP primers. The use of MSTP for linkage analysis greatly reduces the number of PCR reactions. Up to five primer pairs can be multiplexed together in the same reaction. At present, a set of 148 STRP markers spaced at an average genetic distance of 28 cM throughout the autosomal genome can be analyzed in 37 sets of multiplexed amplification reactions. We have automated the analysis of these patterns for linkage using software that both detects the STRP banding pattern and determines their sizes. This information can then be exported in a user-defined format from a database manager for linkage analysis.