Cis-trans isomerism in naphthoquinones: interconversion and participation in oxidative phosphorylation

Synthetic phylloquinone was resolved into cis and trans isomers by thin-layer chromatography. The two isomers had identical ultraviolet spectra characteristic of vitamin K(1) and were differentiated by nuclear-magnetic-resonance spectroscopy on the basis of the displacement of the peak corresponding to the olefinic methyl group in the naphthoquinone side chain. Studies on the restoration of electron transport coupled to phosphorylation in irradiated preparations of Mycobacterium phlei showed that only the trans isomer was active with substrates linked to nicotinamide-adenine dinucleotide. The purified trans phylloquinone was enzymatically converted to the cis isomer. Under similar conditions, cis vitamin K(1) gave rise to the trans-naphthoquinone. The natural naphthoquinone of M. phlei vitamin MK(9)(II-H) was similarly resolved into cis and trans isomers.     

Cell growth with trans fatty acids is affected by adenosine 3',5'-monophosphate and membrane fluidity

Two positional isomers (9 and 11) of trans octadecenoates did not support growth on glucose of an Escherichia coli mutant that requires unsaturated fatty acids. However, the trans fatty acids provided sufficient fluidity to produce much higher cell yields when the concentration of adenosine 3',5'-monophosphate was raised. The effectiveness of the trans acids rose from 0 to 1 cell per femtomole to 15 to 20 cells per femtomole as the concentration of adenosine 3',5'-monophosphate was increased. The corresponding cis positional isomers supported high yields (35 to 40 cells per femtomole) independent of supplementation. The enhanced growth with adenosine 3',5'-monophosphate supplementation is not due to an increased uptake and incorporation of the trans isomers relative to the cis isomers, since the 9-trans isomer was incorporated more rapidly than the 9-cis isomer into the membrane phospholipids under all growth conditions and represented 21 +/- 2 mole percent of the acids. The finding that cells growing with trans fatty acid isomers have a higher requirement for adenosine 3',5'-monophosphate may indicate that some fatty acids can alter the metabolic regulation normally exerted by the cyclic nucleotide.     

氯菊酯的毛细管气相色谱分析

介绍了用 SE-52毛细管柱气相色谱、FID 检测器,以癸二酸二辛酯为内标的氯菊酯定量分析方法。本方法成功地分离了氯菊酯的顺、反异构体。测得方法变异系数为0.45%,氯菊酯顺、反异构体的比例为43.6:56.4,平均添加回收率为100.10%,线性相关系数为0.9988。     

Clarification of the chemical status of the pink bollworm sex pheromone

Propylure, 10-n-propyl-trans-5,9-tridecadienyl acetate, and deet, N,N,-diethyl-m-tolumide, were previously reported as the sex pheromone and a sex pheromone activator, respectively, of the pink bollworm. Neither chemical in three extracts of female moth abdomen tips could be detected by gas-liquid chromatographic analysis. These compounds, alone or in combination, exhibited little or no biological activity in the laboratory or in the field. Hexalure, cis-7-hexadecenyl acetate, a synthetic attractant for pink bollworm males, could not be detected in female moth abdomen tip extracts. The pink bollworm sex pheromone was identified as a mixture of cis,cis and cis,trans isomers of 7,11-hexadecadienyl acetate.     

核酶及其分子药物设计与应用

酶是８０年代初期发现的具有自催化活性的ＲＮＡ片从核酸水平来破坏对人体不利的基因在人细胞内的表达,这是一种比较专一,且对人体危害相对较小的一种方式,经过改诉核酶不仅能起顺式作用,更重要的是也能以反式作用,这样就使得人们能够设计出针对ＲＮＡ的各种具有治疗作用的核酶,该文着重介绍具锤头型结构域和发夹型结构域的２类核酶的设计,及核酶作为治疗药物所要考虑的一些问题。     

亚硝酸分子的几何异构现象

本文用半经验分子轨道法对亚硝酸分子进行构象分析,同最小分子能量对应,平衡几何构型以顺式稳定,以E_(LUMO)和E_(HUMO)—E_(LUMO)作为得电子指标,对氧化还原稳定性来说,反式的构型大于顺式。     

Self-inhibitor of bean rust uredospores: methyl 3,4-dimethoxycinnamate

Two germination inhibitors from bean rust uredospores were identified as the cis and trans isomers of methyl 3,4-dimethoxycinnamate. They appear to be the "self-inhibitors" previously described from these spores.     

Identification of the germination self-inhibitor from wheat stem rust uredospores

Two germination inhibitors from wheat rust uredospores were identified as the cis and trans isomers of methyl 4-hydroxy-3-methoxycinnamate (methyl ferulate). They are the self-inhibitors from these spores described previously.     

Transient homologous chromosome pairing marks the onset of X inactivation

Mammalian X inactivation turns off one female X chromosome to enact dosage compensation between XX and XY individuals. X inactivation is known to be regulated in cis by Xite, Tsix, and Xist, but in principle the two Xs must also be regulated in trans to ensure mutually exclusive silencing. Here, we demonstrate that interchromosomal pairing mediates this communication. Pairing occurs transiently at the onset of X inactivation and is specific to the X-inactivation center. Deleting Xite and Tsix perturbs pairing and counting/choice, whereas their autosomal insertion induces de novo X-autosome pairing. Ectopic X-autosome interactions inhibit endogenous X-X pairing and block the initiation of X-chromosome inactivation. Thus, Tsix and Xite function both in cis and in trans. We propose that Tsix and Xite regulate counting and mutually exclusive choice through X-X pairing.     

Alcohol dehydrogenase in maize: genetic control of enzyme activity

A gene (Adhr(r)) which controls the activity of alcohol dehydrogenase in the scutellum of maize has been found. This gene is not allelic to the Adh(1) locus, which specifies the charge of the enzyme molecule and hence its migration rate. The two genes are linked and located about 17 crossover units apart. The Adh(r)(N) allele specifies equal activities of both the Adh(1)(S) and Adh(1)(F) products. The Adh(r)(L) allele gives lower activities of the Adh(1)(S) products only and operates in both the cis and the trans configurations.     

Optical switching and image storage by means of azobenzene liquid-crystal films

Liquid crystals are promising materials for optical switching and image storage because of their high resolution and sensitivity. Azobenzene liquid crystals (LCs) have been developed, in which azobenzene moieties play roles as both mesogens and photosensitive chromophores. Azobenzene LC films showed a nematic phase in trans isomers and no LC phase in cis isomers. Trans-cis photoisomerization of azobenzene with a laser pulse resulted in a nematic-to-isotropic phase transition with a rapid optical response of 200 microseconds.     

α-乙氧羰基环十二烷基羧酸酯的合成及其植物生长调节活性

以环十二酮为原料，经乙氧羰基化，酮羰基的选择性还原、酯化合成了10个α-乙氧羰基环十二烷基羰酸酯。它们的结构经IR，1HNMR，MS和元素分析确证。用1HNMR还证实了顺反异构体的存在。生测结果表明，其中的一些具有良好的促进植物生根的活性。     

C-cadherin ectodomain structure and implications for cell adhesion mechanisms

Cadherins are transmembrane proteins that mediate adhesion between cells in the solid tissues of animals. Here we present the 3.1 angstrom resolution crystal structure of the whole, functional extracellular domain from C-cadherin, a representative "classical" cadherin. The structure suggests a molecular mechanism for adhesion between cells by classical cadherins, and it provides a new framework for understanding both cis (same cell) and trans (juxtaposed cell) cadherin interactions. The trans adhesive interface is a twofold symmetric interaction defined by a conserved tryptophan side chain at the membrane-distal end of a cadherin molecule from one cell, which inserts into a hydrophobic pocket at the membrane-distal end of a cadherin molecule from the opposing cell.     

Isolation of trans-Aconitic Acid from the Moss Mnium affine

The water-soluble substance occurring in high concentration (up to 6 percent of the dry weight) in Mnium affine Bland. and forming the main fraction of the plant acids there, has been identified as trans-aconitic acid by nine different criteria. Evidence is presented in favor of the concept that the trans form in this case is the natural isomer and not an artifact derived from cis-aconitic acid. Information is given on the distribution of aconitic acid in other mosses and in liverworts.     

Stereospecific action of pyrethroid insecticides on the gamma-aminobutyric acid receptor-ionophore complex

The potent alpha-cyano-3-phenoxybenzyl pyrethroids, including cypermethrin, deltamethrin, and fenvalerate, act stereospecifically to inhibit binding to rat brain synaptic membranes of sulfur-35-labeled t-butylbicyclophosphorothionate, a new radioligand for the picrotoxinin binding site. Scatchard analysis indicates that picrotoxinin inhibition of t-butylbicyclophosphorothionate binding is competitive whereas cypermethrin inhibition possibly involves a closely associated site in the gamma-aminobutyric acid receptor-ionophore complex. Studies with 37 pyrethroids reveal an absolute correlation, that is, no false positives or negatives, between mouse intracerebral toxicity and in vitro inhibition: all toxic cyano compounds but none of their nontoxic stereoisomers are inhibitors; cis isomers are more potent than trans isomers as both toxicants and inhibitors; and noncyano pyrethroids are much less potent or are inactive.     

Photoregulation of an enzymic process by means of a light-sensitive ligand

A specific inactivator of chymotrypsin, p-azophenyldiphenylcarbamyl chloride, exists as two geometric isomers, cis and trans, which are interconvertible by means of light. The cis-isomer is five times more reactive than the more stable trans-isomer, and is obtained by exposure of the latter to light of 320 nanometer wavelength. The trans-isomer can be regained by exposure of the cis-isomer to light of 420 nanometer wavelength. This interconversion can be made to occur in aqueous solution in the presence of the enzyme under conditions in which the trans-isomer reacts relatively slowly with chymotrypsin. Thus, it is possible to regulate the rate of inactivation of chymotrypsin by using light of the appropriate wavelength. This system is presented as a model for some of the light-sensitive metabolic systems present in living organisms.     

Untangling desmosomal knots with electron tomography

Cell adhesion by adherens junctions and desmosomes relies on interactions between cadherin molecules. However, the molecular interfaces that define molecular specificity and that mediate adhesion remain controversial. We used electron tomography of plastic sections from neonatal mouse skin to visualize the organization of desmosomes in situ. The resulting three-dimensional maps reveal individual cadherin molecules forming discrete groups and interacting through their tips. Fitting of an x-ray crystal structure for C-cadherin to these maps is consistent with a flexible intermolecular interface mediated by an exchange of amino-terminal tryptophans. This flexibility suggests a novel mechanism for generating both cis and trans interactions and for propagating these adhesive interactions along the junction.     

Anabaena sensory rhodopsin: a photochromic color sensor at 2.0 A

Microbial sensory rhodopsins are a family of membrane-embedded photoreceptors in prokaryotic and eukaryotic organisms. Structures of archaeal rhodopsins, which function as light-driven ion pumps or photosensors, have been reported. We present the structure of a eubacterial rhodopsin, which differs from those of previously characterized archaeal rhodopsins in its chromophore and cytoplasmic-side portions. Anabaena sensory rhodopsin exhibits light-induced interconversion between stable 13-cis and all-trans states of the retinylidene protein. The ratio of its cis and trans chromophore forms depends on the wavelength of illumination, thus providing a mechanism for a single protein to signal the color of light, for example, to regulate color-sensitive processes such as chromatic adaptation in photosynthesis. Its cytoplasmic half channel, highly hydrophobic in the archaeal rhodopsins, contains numerous hydrophilic residues networked by water molecules, providing a connection from the photoactive site to the cytoplasmic surface believed to interact with the receptor's soluble 14-kilodalton transducer.     

Single-molecule optomechanical cycle

Light-powered molecular machines are conjectured to be essential constituents of future nanoscale devices. As a model for such systems, we have synthesized a polymer of bistable photosensitive azobenzenes. Individual polymers were investigated by single-molecule force spectroscopy in combination with optical excitation in total internal reflection. We were able to optically lengthen and contract individual polymers by switching the azo groups between their trans and cis configurations. The polymer was found to contract against an external force acting along the polymer backbone, thus delivering mechanical work. As a proof of principle, the polymer was operated in a periodic mode, demonstrating for the first time optomechanical energy conversion in a single-molecule device.