Small molecule activators of sirtuins extend Saccharomyces cerevisiae lifespan

In diverse organisms, calorie restriction slows the pace of ageing and increases maximum lifespan. In the budding yeast Saccharomyces cerevisiae, calorie restriction extends lifespan by increasing the activity of Sir2 (ref. 1), a member of the conserved sirtuin family of NAD(+)-dependent protein deacetylases. Included in this family are SIR-2.1, a Caenorhabditis elegans enzyme that regulates lifespan, and SIRT1, a human deacetylase that promotes cell survival by negatively regulating the p53 tumour suppressor. Here we report the discovery of three classes of small molecules that activate sirtuins. We show that the potent activator resveratrol, a polyphenol found in red wine, lowers the Michaelis constant of SIRT1 for both the acetylated substrate and NAD(+), and increases cell survival by stimulating SIRT1-dependent deacetylation of p53. In yeast, resveratrol mimics calorie restriction by stimulating Sir2, increasing DNA stability and extending lifespan by 70%. We discuss possible evolutionary origins of this phenomenon and suggest new lines of research into the therapeutic use of sirtuin activators.     

Assessing the redundancy of MADS-box genes during carpel and ovule development

Carpels are essential for sexual plant reproduction because they house the ovules and subsequently develop into fruits that protect, nourish and ultimately disperse the seeds. The AGAMOUS (AG) gene is necessary for plant sexual reproduction because stamens and carpels are absent from ag mutant flowers. However, the fact that sepals are converted into carpelloid organs in certain mutant backgrounds even in the absence of AG activity indicates that an AG-independent carpel-development pathway exists. AG is a member of a monophyletic clade of MADS-box genes that includes SHATTERPROOF1 (SHP1), SHP2 and SEEDSTICK (STK), indicating that these four genes might share partly redundant activities. Here we show that the SHP genes are responsible for AG-independent carpel development. We also show that the STK gene is required for normal development of the funiculus, an umbilical-cord-like structure that connects the developing seed to the fruit, and for dispersal of the seeds when the fruit matures. We further show that all four members of the AG clade are required for specifying the identity of ovules, the landmark invention during the course of vascular plant evolution that enabled seed plants to become the most successful group of land plants.     

Modeling and Solving Material Resources Allocation and Distribution with OR Based and AI Guided Method

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纳米Ag-Cu合金的Ag和Cu析出与晶粒长大行为研究

纳米晶材料(nc-)首先由Gleiter和他的合作者提出,并用惰性气体淀积法(IGC)所获得.这些纳米颗粒在真空下原位加压成型.纳米晶材料的平均直径一般采用X-射线衍射法测定.引起X射线衍射峰展宽有两个因素:小的颗粒直径和晶体缺陷造成的内应力.在惰性气体淀积法(IGC)过程中,由于金属蒸气迅速冷却凝聚,可能形成过饱和固溶体而处于非平衡状态;另一方面金属合金蒸气中的溶质原子浓度的涨落会改变溶质在纳米颗粒中的浓度,这都可能使X射线衍射峰展宽.因此除用X射线衍射法外,结合其他方法是必要的.AgCu合金是研究这一效应的最佳材料.Kumpmann用示差热分析(DSC)来研究nc-AgCu合金,观察到大的放热反应,这与过饱和α-Ag和α-Cu的析出有关.     

半群环中的半幂等元

本文提出了半群环的半幂等元的概念。在[2]中,作者已提出了群环的半幂等元的概念。