キイロショウジョウバエ由来のチオレドキシン還元酵素のC未端テトラペプチド配列は、ヒト肺由来のチオレドキシン還元酵素では酸化還元活性を示さない

The isozymes of mammalian thioredoxin reductase (TrxR) contain the penultimate selenocysteineresidue (SeCys) in the redox-active C-terminal tetrapeptide, -Gly-Cys-SeCys-Gly (end). Amutant form of the mammalian enzyme TrxR-X498C in which SeCys is replaced with Cys showsa dramatically decreased catalytic activity, suggesting that SeCys residue plays an integral role inthe catalysis. In contrast, TrxR of the fruit fly, Drosophila melanogaster, has no selenium in the corresponding C-terminal redox sequence, which instead of SeCys has flanking serine residues in the terminal sequence, -Ser-Cys-Cys-Ser (end). Because the catalytic activity of Dm-TrxR is comparable to that of the mammalian selenoenzyme, we introduced the serine residues at the corresponding positions of the recombinant TrxR-X498C and mimicked the redox center of the fruit fly TrxR. However, the catalysis remained as low as the Cys mutant of the selenoenzyme, suggesting that the additional structural features are still required for the tetrapeptide to function as a redox center. MOPAC calculation suggested that the complete motif might involve the hexapeptide sequence, which includes a proline residue, -Pro-X-Ser-Cys-Cys-Ser (end). The proline-containing motif is conserved among other insect TrxRs such as those of honeybee and fruit fly.ほ乳類チオレドキシン還元酵素はＣ末端配列-Gly-Cys-SeCys-Gly（end）の後ろから２番目にセレノシステイン（SeCys）残基を持つ．SeCys をシステインに変換すると酵素の活性は大きく低下するので，SeCys 残基が触媒活性に必須であることが分かる．これに対してキイロショウジョウバエのチオレドキシン還元酵素（Dm-TrxR）のＣ末端配列にはセレンが含まれず，システイン残基の対が２つのセリンに挟まれた配列-Ser-Cys-Cys-Ser (end）を持つ．それでも Dm-TrxR はほ乳類のセレン含有酵素と同程度の触媒能を示す．われわれはヒト肺チオレドキシン還元酵素に Dm-TrxR のＣ末端テトラペプチド配列を導入してその効果を調べた．しかし，酵素活性はまったく上昇せず，Dm-TrxR のＣ末端のテトラペプチド配列-Ser-Cys-Cys-Ser だけでは Cys 残基のチオール基を活性化する効果はなかった．そこで，分子軌道計算 MOPAC を用いて酸化還元機能を担うためのＣ末端配列モチーフを探索した．その結果，テトラペプチドにさらに２つ先のプロリンまでを含めた Pro-X-Ser-Cys-Cys-Ser（end）により初めて酸化還元モチーフとして機能する可能性が示唆された．Pro を含むこの配列モチーフはミツバチや蚊などほかの昆虫の TrxR でも保存されてい

Design of a semiconductor ferromagnet in a quantum dot artificial crystal

We present the theoretical design of quantum dot (QD) artificial ferromagnetic crystals. The electronic structure calculations based on local spin density approximation (LSDA) show that our designed QD artificial crystal from a structure comprising the crossing 0.104-micrometer-wide InAs quantum wires (an effective Kagome lattice) has flat band characteristics. Our examined QD artificial crystal has the ferromagnetic ground state when the flat band is half-filled, even though it contains no magnetic elements. The ferromagnetic and the paramagnetic state can be freely switched by changing the electron filling via a gate voltage.Comment: 12 pages, 3 figures included. For related information, visit http://www.brl.ntt.co.jp/people/tamura

Identification of Ornithine-lactam Converted from Arginine in Streptomyces incarnatus NRRL8089

Sinefungin is a nucleoside antibiotic, in which a molecule of L-ornithine is linked to the 5' end of adenosine through a C-C bond. The antibiotic was isolated from the culture broth of Streptomyces incarnatus. For the purpose of detecting intermediate of sinefungin biosynthesis, resting cell suspensions were incubated with supplemental L-arginine, and L-ornithine. 50mM Arginine was converted to a compound X that has low polarity. 50mM ornithine was not converted and remained in reaction solution. Compound X was purified using HPLC, and analyzed using (1)H-NMR and FAB-MS. These analyses showed that a compound X is "ornithine-lactam" (Mw＝114), which has a structure of circularized ornithine. These results indicated that S. incarnatus has an enzyme that converts arginine to ornithine-lactam. Such an enzyme has never been reported, and suggested that it may be relevant to sinefungin biosynthesis.シネフンギンは抗真菌，抗マラリア活性を有する核酸系抗生物質であり，放線菌 S. incarnatus により生合成される．シネフンギンはアデノシンとオルニチンがＣﾝＣ結合した構造であり，無細胞抽出液での取り込み実験からＬﾝアルギニンと ATP から生合成されると推測される．Ｌﾝアルギニン，Ｌﾝオルニチンを S. incarnatus の休止菌体反応系への投与を行いシネフンギン中間体の探索を行った．その結果50ﾋアルギニンは24時間以内に低極性化合物へと変換された．一方50ﾋオルニチンは変換されず反応液中に残存した．HPLC で化合物を精製し，1HﾝNMR，FABﾝMS での分析の結果オルニチン環状モノペプチド，「オルニチンラクタム」（分子量114）であることを明らかにした．この結果は S. incarnatus がアルギニンからオルニチンラクタムへの変換酵素を有する事を示唆する．このような酵素の報告例はこれまでになく，ニ次代謝酵素であることが示唆され，シネフンギン生合成との関連性に興味が持たれる

ヒト由来チオキドキシン還元酵素のカルボキシル末端配列の酸化還元状態の半経験的分子軌道計算

Semiempirical molecular orbital calculation (MOPAC) was used to estimate the enthalpy difference (ΔH) between the reduce and oxidized states of the C-terminal rebox center of human thioredoxin reductase. Heat of formation was computed by WinMOPAC 3.5Pro for the model peptides, N-Acetyl-Ser-Ile-Leu-Gly-X1-X2-Gly, whose-X1-X2-sequence was-Cys SeCys-(natural sequence), -SeCys-Cys-(reverse sequence), -Cys-Cys, and-SeCys-SeCys-. Calculation by Hamiltonian AM1 and PM3 agreed that the oxidized state with selenosulfide bonds and a diselenide bond were more favoralbe than their reduced states. Only the peptide that contained-Cys-Cys-sequence was shown to have lower enthalpy when the two Cys were in the reduced form. It has been reported that substitution of SeCys498 to Cys results in the mujtant TrxRs retaining only about 1% of the enzyme activity. The results of computational estimation supported the experimental hypothesis that the inactivation by SeCys498Cys mutation was due to the unfavorable formation of disulfide bond between Cys497-Cys498.ヒトのチオレドキシン還元酵素（TrxR）のカルボキシル末端配列の酸化還元に伴うエンタルピー変化を計算した。半経験的分子軌道計算 WinMOPAC 3.5Pro を用いてモデルペプチド、N-Ac-Ser-Ile-Leu-Gln-Ala-Gly-X1-X2-Gly の生成熱を算出した。X1,X2のアミノ酸配列は-SeCys-Cys、 -Cys-SeCys-、 -SeCys-SeCys-、 -Cys-Cys- のいずれかで、それぞれ酸化状態と還元状態を計算し、そのエンタルピー差を求めた。ハミルトニアン AM1 と PM3は同じ傾向の計算結果を示し、セレノスルフィドまたはジセレニドを形成するペプチドは酸化状態でより安定化するのに対して-Cys-Cys-の配列を持つペプチドは還元型の方が安定的であることを示した。ほ乳類の TrxR の SeCys498 を Cys に置換すると酵素活性が1%程度にまで低下することが報告されている。これは、変異酵素が -Cys497-Cys498- 間で酸化的架橋を形成しにくいからと考察されていたが、今回の分子軌道計算の結果は、この仮説を支持している

Purification and Characterization of l-Methionine Decarboxylase from Streptomyces sp. 590

L-Methionine decarboxylase [EC 4.1.1.57] catalyzes the decarboxylation of L-methionine and is a pyridoxal 5’-phosohate(PLP)-dependent enzyme. L-Methionine decarboxylase has been purified 630-fold by DEAE-Toyopearl 650M, Phenyl-Toyopearl 650M and Sephacryl S-300 column chromatographies from Streptomyces sp.590. The enzyme has a dimeric structure with identical subunits of Mr 60,000. This enzyme shows optimum activity at pH7.0 and 45°C, and is stable between pH5.7 and pH9.0. L-Methionine decarboxylase has antitumor activity against RERF-LC-AI and HeLa cells. Ten N-terminal amino acid sequence of L-methionine decarboxylase was determined, and the sequence showed no homology with other reported proteins

Craving for Gambling Predicts Income-Generating Offenses : A Pathways Model of a Japanese Prison Population

The links between gambling and criminal offenses have been frequently reported, but the pathways from gambling to a particular offense have not. Our study applied a pathways model to predict participants’ income-generating, drug-related, and violent offenses stemming from their craving for gambling. The participants were 332 male inmates in a Japanese local prison. They answered questionnaires on gambling behavior, alcohol addiction, Internet addiction, impulsivity, and psychopathy. Their official records with information on their current offense, sentence length, number of imprisonments, and length of education were also analyzed. The results show that 38.55% (n = 128) of the participants had a probable gambling disorder, a rate of problem gambling at least four times higher than that among the general Japanese population. Furthermore, their craving for gambling predicted their income-generating offenses, but not their drug-related and violent offenses. Their craving for gambling can thus be linked to their financial issues, rather than their emotional and impulsive issues. The pathways model explained the path not only from addiction/psychopathy to gambling, but also from gambling to committing an income-generating offense