Is (9Z)‐“meso”‐zeaxanthin optically active?

The question raised in the title was answered. (3R, 3'S)-meso-Zeaxanthin was submitted to iodine catalyzed photochemical stereoisomerisation. The enantiomeric (9Z) and (9'Z) geometrical isomers were isolated by semipreparative HPLC and separated as diastereomeric dicarbamates on a chiral column only. Cleavage of the carbamate could not be effected. CD-Spectra of (1"S, 1"S)- and (1"R, 1"R)-dicarbamates of geometrical isomers of (3R, 3'R)- and (3R, 3'S)-meso-zeaxanthin were systematically studied and the contribution from the carbamate moieties revealed. It was concluded that (9Z, 3R, 3'S)-"meso"-zeaxanthin, in spite of having no symmetry elements, is optically inactive. The result has been rationalised in line with the current hypothesis on the origin of carotenoid CD spectra.     

“整合物种概念”和“分化路上的物种”

已有的各个物种概念对物种的认识类似盲人摸象, 只包含了物种的某一个方面; 而一个分化后期的成熟物种应涵盖了所有的物种概念。但是, 尚未到达分化后期的物种往往又已开始新一轮的物种分化; 自然中存在的多数“物种”处于分化路上。这种循环往复连续分化产生的物种, 存在种间生殖隔离不彻底、基因流频繁发生、网状进化突出等现象。此外, 对于不同的物种对, 最早开始分化的基因以及不同物种概念所要求的条件的分化顺序不是统一的, 而是随机的。定义一个适合所有“分化路上的物种”概念存在较大困难。但是, 应采用尽可能多的物种概念来界定分化路上的物种、发表新种和进行分类处理; 也应承认种间可能广泛存在不完全的生殖隔离和有限的基因流, 即有不属于两个物种群体的杂交或回交个体的存在。这样划分的物种比只依据一个物种概念认定的物种具有更高的客观性和科学性。     

Revisiting “what do tadpoles really eat?” A 10‐year perspective

相似文献   

“地衣”词考

本文考证了中国先秦时期到清末古籍中对“地衣”的解释;其中有共生学意义的“地衣”一词,是在清代李善兰的《植物学》一书中被提出的。     

Étienne Geoffroy St.‐Hilaire: father of “evo‐devo”?

SUMMARY In the early decades of the nineteenth century, the most important disagreement among comparative anatomists was not evolution versus "special creation" but between advocates of "transcendental morphology" and those of teleological anatomy—form versus function. In France this dichotomy was represented by the 1830–1832 public debate between Geoffroy St.-Hilaire (form) and Cuvier (function). Geoffroy's aim was to establish links of homology (known to him as "analogies") between the four "embranchements" into which Cuvier had divided the animal kingdom. Despite the fanciful nature of some of his homologies, Geoffroy, who was guided by his " principe de connections ," set in motion a school of morphology, some of whose conclusions, notably the homology of the dorsal surface of segmented invertebrates with the ventral surface of vertebrates, has been corroborated by recent studies in developmental genetics.     

Does Perinatal ω‐3 Polyunsaturated Fatty Acid Deficiency Increase Appetite Signaling?

Objective: To investigate the effect of maternal dietary ω‐3 polyunsaturated fatty acid (PUFA) deficiency and repletion on food appetite signaling. Research Methods and Procedures: Sprague‐Dawley rat dams were maintained on diets either supplemented with (CON) or deficient in (DEF) ω‐3 PUFA. All offspring were raised on the maternal diet until weaning. After weaning, two groups remained on the respective maternal diet (CON and DEF groups), whereas a third group, born of dams fed the DEF diet, were switched to the CON diet (REC). Experiments on food intake began when the male rats reached 16 weeks of age. Food intake was stimulated either by a period of food restriction, by blocking glucose utilization (by 2‐deoxyglucose injection), or by blocking β‐oxidation of fatty acids (by β‐mercaptoacetate injection). Results: DEF animals consumed more than CON animals in response to all stimuli, with the greatest difference (1.9‐fold) demonstrated following administration of 2‐deoxyglucose. REC animals also consumed more than CON animals in response to food restriction and 2‐deoxyglucose but not to β‐mercaptoacetate. Discussion: These findings indicate that supply of ω‐3 PUFA, particularly during the perinatal period, plays a role in the normal development of mechanisms controlling food intake, especially glucoprivic (i.e. reduced glucose availability) appetite signaling. Dietary repletion of ω‐3 PUFA from 3 weeks of age restored intake responses to fatty acid metabolite signaling but did not reverse those in response to food restriction or glucoprivic stimuli.     

Extended π‐Bridge in Organic Dye‐Sensitized Solar Cells: the Longer,the Better?

The elongation of π‐conjugated bridges between the donor (D) and the acceptor (A) represents a feasible strategy towards enhancement of light‐harvesting in both breadth and depth of organic D‐π‐A dyes suitable for nanocrystalline TiO₂‐based dye‐sensitized solar cells (DSSCs). Here, a series of organic dyes with elongating conjugated bridges is synthesized and characterized. DSSC devices employing a cobalt (II/III) redox electrolyte are fabricated using these dyes as light‐harvesting sensitizers. Compared to a dye with the 3,4‐ethylenedioxythiophene (EDOT) linker ( G188 ), the three counterparts with further extended π‐bridges present gradually red‐shifted electronic absorption spectra and a persistent decrease in oxidation potential. The photocurrent action spectra show that the extension of π‐conjugated bridges decreases the open‐circuit photovoltage. The best performance is shown in G268 with a short‐circuit photocurrent density (J_sc) of 16.27 mA cm², an open‐circuit photovoltage (V_oc) of 0.83 V, and a fill factor (FF) of 0.67, corresponding to an overall conversion efficiency of 9.24%. Unexpectedly, G270, which has with the longest π‐bridge , showed the lowest J_sc, V_oc, and efficiency.     

“超级真菌”耳念珠菌研究进展

耳念珠菌Candida auris也被称为“超级真菌”,是近年来出现的一种人体病原真菌新物种,临床分离株通常具有多重耐药和高致死率等特征。2009年日本首次报道耳念珠菌之后,其感染病例在多个国家呈现出爆发式增长。目前已报道的病例分布在全球五大洲27个国家,包括中国。耳念珠菌感染给临床诊断和防控以及人类健康带来了巨大的挑战。本文从该菌临床分离菌株的生物学、遗传变异分化及耐药特征等方面入手,围绕分子流行病学、基因组特征、毒性因子和耐药性等方面系统地综述了近年来国内外取得的相关进展,并探讨了我国耳念珠菌感染的诊断、治疗和预防的措施。     

Gibt es einen „Duft der MHC‐Gene“?

MHC‐Genes: Do they influence the choice of partners via olfactory signals? Behavioral experiments in mice and humans suggest that genes of the major histocompatibilty complex (MHC) may be important for the differentiation of self and non‐self during mate choice. While this correlation is well documented for certain mouse strains, it is controversial for humans. Signal transfer between potential partners is considered to occur via the production of MHC‐dependent olfactory cues by a sender and their recognition by olfaction in the recipient. It is shown that in mice and humans the overall bouquet of volatiles is not and the pattern of peptides in mice is only marginally influenced by the MHC genes. However, in mice, olfactory cues without MHC contribution appear to play a role in mate choice, in that the profile learned from the parents during rearing is compared with the distinct profile of a potential partner, which is in turn selected for mating. Such olfactory differentiation between close relatives and potential mates without MHC‐contribution may also operate unconsciously in humans.     

“New”‐clear functions of PDK1: Beyond a master kinase?

Activation of cytosolic phosphoinositide-3 kinase (PI-3K) signaling pathway has been well established to regulate gene expression, cell cycle, and survival by feeding signals to the nucleus. In addition, strong evidences accumulated over the past few years indicate the presence of an autonomous inositol lipid metabolism and PI-3K signaling within the nucleus. Much less, however, is known about the role and regulation of this nuclear PI-3K pathway. Components of the PI-3K signaling pathway, including PI 3-kinase and its downstream kinase Akt, have been identified at the nuclear level. Consistent with the presence of a complete PI-3K signaling pathway in the nucleus, we have recently found that phosphoinositide-dependent kinase 1 (PDK1), a kinase functioning downstream of PI-3K and upstream of Akt, is a nucleo-cytoplasmic shuttling protein. In the present review, we update our current knowledge on the regulatory mechanisms and the functional roles of PDK1 nuclear translocation. We also summarize some of the kinase-independent activities of PDK1 in cell signaling.     

What is the role of the second “structural” NADP+‐binding site in human glucose 6‐phosphate dehydrogenase?

Human glucose 6-phosphate dehydrogenase, purified after overexpression in E. coli, was shown to contain one molecule/subunit of acid-extractable "structural" NADP+ and no NADPH. This tightly bound NADP+ was reduced by G6P, presumably following migration to the catalytic site. Gel-filtration yielded apoenzyme, devoid of bound NADP+ but, surprisingly, still fully active. Mr of the main component of "stripped" enzyme by gel filtration was approximately 100,000, suggesting a dimeric apoenzyme (subunit Mr = 59,000). Holoenzyme also contained tetramer molecules and, at high protein concentration, a dynamic equilibrium gave an apparent intermediate Mr of 150 kDa. Fluorescence titration of the stripped enzyme gave the K d for structural NADP+ as 37 nM, 200-fold lower than for "catalytic" NADP+. Structural NADP+ quenches 91% of protein fluorescence. At 37 degrees C, stripped enzyme, much less stable than holoenzyme, inactivated irreversibly within 2 d. Inactivation at 4 degrees C was partially reversed at room temperature, especially with added NADP+. Apoenzyme was immediately active, without any visible lag, in rapid-reaction studies. Human G6PD thus forms active dimer without structural NADP+. Apparently, the true role of the second, tightly bound NADP+ is to secure long-term stability. This fits the clinical pattern, G6PD deficiency affecting the long-lived non-nucleate erythrocyte. The Kd values for two class I mutants, G488S and G488V, were 273 nM and 480 nM, respectively (seven- and 13-fold elevated), matching the structural prediction of weakened structural NADP+ binding, which would explain decreased stability and consequent disease. Preparation of native apoenzyme and measurement of Kd constant for structural NADP+ will now allow quantitative assessment of this defect in clinical G6PD mutations.     

新医学是解决人类健康问题的真正钥匙——需“精准”理解奥巴马的“精准医学计划”

2015年年初,美国总统奥巴马在国情咨文中提出了一个预算2.15亿美元的“精准医学计划”,希望以此“引领一个医学时代”。新闻一经发布,“精准医学”立刻成为了媒体和百姓嘴边的热词,受此影响国内亦有不少人士纷纷为美国总统的这一计划点“赞”。有人用“医学革命”来形容它,有人用“开创性”来抬高它,还有一个传闻,受奥巴马“精准医学计划”的影响,中国将在15年内投入600亿元人民币启动并发展中国版的“精准医学计划”。对此,有人提出了质疑,美国版精准医学计划是否符合中国国情?是否存在“水土不服”的可能?直接套用美国总统的智慧能否解决具有中国特色的实际问题?争论由此引发一个让人思考的问题,究竟什么才是现代医学的核心?在盲目堆钱的行动前,我们确实有必要从科学和临床应用的角度来探讨和思考一下现代医学的发展方向。 为了能“精准”地看到问题的实质,我将从当下时髦并且相关的词汇谈起,通过梳理,期待找出解决人类健康问题的真正钥匙。     

Who Is the King? The α‐Hydroxy‐β‐oxo‐α,β‐enone Moiety or the Catechol B Ring: Relationship between the Structure of Quercetin Derivatives and Their Pro‐Oxidative Abilities

Quercetin and other flavonoids have been reported to exhibit both antioxidant and pro‐oxidant properties. Most studies about the pro‐oxidative ability were conducted in the presence of metal ions, and the essential functional moiety of quercetin responsible for the pro‐oxidative effect is still unclear. In this study, we evaluated the pro‐oxidative abilities in the absence of metal ions of two quercetin derivatives, i.e., quercetin‐3′‐O‐β‐D ‐glucoside ( 1 ) and quercetin‐3‐O‐β‐D ‐glucoside ( 2 ), by assessing DNA cleavage and HO^.‐radical production. The binding mode between these compounds and DNA was studied by fluorescence and viscometric titrations. The results showed that 1 can efficiently induce oxidative damage to plasmid DNA, while 2 shows poor activity. Both 1 and 2 bind to DNA via groove‐binding. These results proved that the α‐hydroxy‐β‐oxo‐α,β‐enone moiety contributes to the pro‐oxidative activity of quercetin.     

Can the combination of electrochemical regeneration of NAD+, selectivity of L‐α‐amino‐acid dehydrogenase,and reductive amination of α‐keto‐acid be applied to the inversion of configuration of a L‐α‐amino‐acid?

The inversion of configuration of L‐alanine can be carried out by combining its selective oxidation in the presence of NAD⁺ and L‐alanine dehydrogenase, electrochemical regeneration of the NAD⁺ at a carbon felt anode, and reductive amination of pyruvate, i.e., reduction of its imino derivative at a mercury cathode, the reaction mixture being buffered with concentrated ammonium/ammonia (1.28M / 1.28M). The dehydrogenase exhibits astonishing activity and stability under such extreme conditions of pH and ionic strength. The main drawback of the process is its slowness. At best, the complete inversion of a 10 mM solution of L‐alanine requires 140 h. A careful and detailed quantitative analysis of each of the key steps involved shows that the enzyme catalyzed oxidation is so thermodynamically uphill that it can be driven efficiently to completion only when both the coenzyme regeneration and the pyruvate reduction are very effective. The first condition is easily fulfilled. Under the best conditions, it is the rate of the chemical reaction producing the imine which controls the whole process kinetically. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 64: 101–107, 1999.