Determination of Chromium(III)and Chromium(VI) by Electrothermal Atomic Absorption Spectrometry after Separation and Preconcentration with Ion Exchange Resins

A sensitive and selective method for the determination of ppb levels of chromium (III) and chromium (VI) in water, based on preconcentration writh a mixture of finely pulverized chelating exchange resin and anion-exchange resin beads has been investigated by electrothermal atomic absorption spectrometry (ETAAS). A sample solution containing 0.1-2.0μg of both chromium (III) and chromiunl (VI) was placed in a polyethylene beaker; then, 20 mg of anion-exchange resin beads (ARB) and 1ml of finely pulverized chelating exchange resin suspension (CRS) were added at pH 6.　The solution was stirred for 20 min and filtered under suction through a glass filter, and the ARB were placed on the pasted surface of a cel1ophaned tape, fixed by sticking another tape on them, and then divided into several sets of six ARB by cutting with ceramics scissors. A sets of six ARB was inserted into a cup-type cuvette for the determination of chromiunl (VI) by ETAAS. The filtrate was then filtered under suction through a membrane filter. A thin circular resin, which was retained on a membrane filter, was fixed by sticking directly with a cellophaned tape and divided into several 3 mm diameter disks by punching. Each disk was used for the deternination of chromium (III) by ETAAS. The effects of commonly occurring foreign ions were investigated. The proposed method based on preconcentration with the exchange resins will be applied to the determination of chromium (III) and chromium (Vl) in water samples

Active Learning Models in Science Classes

研究の第１年次に当たる本年は，理科におけるアクティブラーニング型授業の構造化に向けて，内化と外化の往還を取り入れた授業デザインとその実践に取り組み，具体的実践の蓄積を行った。小学校，中学校，高等学校それぞれで実践を行ったところ，１）学習内容の定着が図られる，２）発展的な内容や未習内容を生徒が主体的に理解することが可能である，３）協働的な学びの場面を加えることで理解の深化が図られる，４）どのような課題に取り組ませるのかといった課題の設定がカギである，５）アクティブラーニングであるか否かを判断するための要素を明らかにする必要がある，などの一定の成果と課題が明らかになった。The purpose of this study is to create active learning models in science classes. As the first-year research, the authors designed the classes which would include a round trip between externalization and internalization, and put them into practice. The designed models were adopted in elementary, junior high and senior high school classes. What have become clear are as the following; 1) Students’ acquisition of the learning contents can be promoted, 2) Students can understand advanced contents proactively, 3) Students’ learning can be deepened by adding collaborative activities, 4) The success or failure to active learning may depend on the quality of the tasks which students work on, 5) It is necessary to clarify the factors to determine active learning

Influence of substitutions of the aromatic amino acid residues around the active site of human APE1

<p><b>Copyright information:</b></p><p>Taken from "Role of the tryptophan residue in the vicinity of the catalytic center of exonuclease III family AP endonucleases: AP site recognition mechanism"</p><p>Nucleic Acids Research 2006;34(5):1552-1563.</p><p>Published online 15 Mar 2006</p><p>PMCID:PMC1408312.</p><p>© The Author 2006. Published by Oxford University Press. All rights reserved</p> () Detection of products of cleavage by wild-type APE1 and its mutant proteins. Substrate DNA (AP-dsDNA: 4.4 pmol), in which the oligonucleotide containing an AP site was 5′ P-labeled, was incubated with the wild-type APE1 or its mutant (0.04 pmol). The DNA products were analyzed by 20% denaturing polyacrylamide gel electrophoresis. () Binding of APE1 and its mutant proteins to the dsDNA containing an AP site (AP-dsDNA). AP-dsDNA (0.45 pmol) was incubated with the wild-type APE1 or its mutants (4.5 pmol). Protein–DNA complex was analyzed by 15% native polyacrylamide gel electrophoresis

The interaction of double-stranded DNA and ExoIII family AP endonuclease

<p><b>Copyright information:</b></p><p>Taken from "Role of the tryptophan residue in the vicinity of the catalytic center of exonuclease III family AP endonucleases: AP site recognition mechanism"</p><p>Nucleic Acids Research 2006;34(5):1552-1563.</p><p>Published online 15 Mar 2006</p><p>PMCID:PMC1408312.</p><p>© The Author 2006. Published by Oxford University Press. All rights reserved</p> A model for recognition of an AP site by the ExoIII family AP endonuclease. () Unbound forms of dsDNA containing an AP site (PDB ID: 1A9I) and human APE1 (PDB ID: 1BIX). The negative charge of the substrate DNA attracts the positively charged region of the enzyme. () An AP site recognition complex. When AP endonuclease encounters an AP site, the tryptophan residue in the vicinity of the catalytic site intercalates into an AP site pocket as an AP site ‘recognizer’. This recognition complex would immediately change into a reaction complex. () A cleavage reaction complex (PDB ID: 1DEW). To cleave on the 5′ side of the AP site, an abasic ribose ring is flipped out from the duplex interior and accommodated into a catalytic pocket with DNA kinking at the AP site

Effects of translocating the tryptophan residue protruding from the surface of the APE1 active site

<p><b>Copyright information:</b></p><p>Taken from "Role of the tryptophan residue in the vicinity of the catalytic center of exonuclease III family AP endonucleases: AP site recognition mechanism"</p><p>Nucleic Acids Research 2006;34(5):1552-1563.</p><p>Published online 15 Mar 2006</p><p>PMCID:PMC1408312.</p><p>© The Author 2006. Published by Oxford University Press. All rights reserved</p> () Detection of AP endonucleolytic activity of APE1 mutants. DNA substrate (AP-dsDNA: 4.4 pmol), in which the oligonucleotide containing an AP site was 5′ P-labeled, was incubated with the wild-type APE1 or its mutant (0.04 pmol). The DNA products were analyzed using a 20% denaturing polyacrylamide gel. () Ability of APE1 mutants to form a complex with the dsDNA containing an AP site. AP-dsDNA (0.45 pmol) was incubated with the wild-type APE1 or its mutant (4.5 pmol). The protein–DNA complexes were analyzed using a 15% native polyacrylamide gel