Imaging nucleophilic substitution dynamics     

Mikosch J  Trippel S  Eichhorn C  Otto R  Lourderaj U  Zhang JX  Hase WL  Weidemüller M  Wester R 《Science (New York, N.Y.)》2008,319(5860):183-186

Anion-molecule nucleophilic substitution (S(N)2) reactions are known for their rich reaction dynamics, caused by a complex potential energy surface with a submerged barrier and by weak coupling of the relevant rotational-vibrational quantum states. The dynamics of the S(N)2 reaction of Cl- + CH3I were uncovered in detail by using crossed molecular beam imaging. As a function of the collision energy, the transition from a complex-mediated reaction mechanism to direct backward scattering of the I- product was observed experimentally. Chemical dynamics calculations were performed that explain the observed energy transfer and reveal an indirect roundabout reaction mechanism involving CH3 rotation.  相似文献   

A conserved family of enzymes that phosphorylate inositol hexakisphosphate     

Mulugu S  Bai W  Fridy PC  Bastidas RJ  Otto JC  Dollins DE  Haystead TA  Ribeiro AA  York JD 《Science (New York, N.Y.)》2007,316(5821):106-109

Inositol pyrophosphates are a diverse group of high-energy signaling molecules whose cellular roles remain an active area of study. We report a previously uncharacterized class of inositol pyrophosphate synthase and find it is identical to yeast Vip1 and Asp1 proteins, regulators of actin-related protein-2/3 (ARP 2/3) complexes. Vip1 and Asp1 acted as enzymes that encode inositol hexakisphosphate (IP6) and inositol heptakisphosphate (IP7) kinase activities. Alterations in kinase activity led to defects in cell growth, morphology, and interactions with ARP complex members. The functionality of Asp1 and Vip1 may provide cells with increased signaling capacity through metabolism of IP6.  相似文献   

Amplification of acetylcholine-binding catenanes from dynamic combinatorial libraries     

Lam RT  Belenguer A  Roberts SL  Naumann C  Jarrosson T  Otto S  Sanders JK 《Science (New York, N.Y.)》2005,308(5722):667-669

Directed chemical synthesis can produce a vast range of molecular structures, but the intended product must be known at the outset. In contrast, evolution in nature can lead to efficient receptors and catalysts whose structures defy prediction. To access such unpredictable structures, we prepared dynamic combinatorial libraries in which reversibly binding building blocks assemble around a receptor target. We selected for an acetylcholine receptor by adding the neurotransmitter to solutions of dipeptide hydrazones [proline-phenylalanine or proline-(cyclohexyl)alanine], which reversibly combine through hydrazone linkages. At thermodynamic equilibrium, the dominant receptor structure was an elaborate [2]-catenane consisting of two interlocked macrocyclic trimers. This complex receptor with a 100 nM affinity for acetylcholine could be isolated on a preparative scale in 67% yield.  相似文献   

A slowly progressive retinopathy in the Shetland Sheepdog     

Karlstam L  Hertil E  Zeiss C  Ropstad EO  Bjerkås E  Dubielzig RR  Ekesten B 《Veterinary ophthalmology》2011,14(4):227-238

Objective To describe a slowly progressive retinopathy (SPR) in Shetland Sheepdogs. Animals Forty adult Shetlands Sheepdogs with ophthalmoscopic signs of SPR and six normal Shetland Sheepdogs were included in the study. Procedure Ophthalmic examination including slit‐lamp biomicroscopy and ophthalmoscopy was performed in all dogs. Electroretinograms and obstacle course‐test were performed in 13 affected and 6 normal dogs. The SPR dogs were subdivided into two groups according to their dark‐adapted b‐wave amplitudes. SPR1‐dogs had ophthalmoscopic signs of SPR, but normal dark‐adapted b‐wave amplitudes. Dogs with both ophthalmoscopic signs and subnormal, dark‐adapted b‐wave amplitudes were assigned to group SPR2. Eyes from two SPR2 dogs were obtained for microscopic examination. Results The ophthalmoscopic changes included bilateral, symmetrical, greyish discoloration in the peripheral tapetal fundus with normal or marginally attenuated vessels. Repeated examination showed that the ophthalmoscopic changes slowly spread across the central parts of the tapetal fundus, but did not progress to obvious neuroretinal thinning presenting as tapetal hyper‐reflectivity. The dogs did not appear seriously visually impaired. SPR2 showed significantly reduced b‐wave amplitudes throughout dark‐adaptation. Microscopy showed thinning of the outer nuclear layer and abnormal appearance of rod and cone outer segments. Testing for the progressive rod–cone degeneration ( prcd )‐mutation in three dogs with SPR was negative. Conclusion Slowly progressive retinopathy is a generalized rod–cone degeneration that on ophthalmoscopy looks similar to early stages of progressive retinal atrophy. The ophthalmoscopic findings are slowly progressive without tapetal hyper‐reflectivity. Visual impairment is not obvious and the electroretinogram is more subtly altered than in progressive retinal atrophy. The etiology remains unclear. SPR is not caused by the prcd‐mutation.  相似文献   

Quantitative und qualitative Veränderungen im A-Horizont von Sandböden nach Umwandlung von Dauergrünland in Ackerland     

Otto Strebel  Jürgen Bttcher  Manfred Eberle  Rudolf Aldag 《植物养料与土壤学杂志》1988,151(5):341-347

Quantitative and qualitative changes in soil properties of A- horizons of sandy soils caused by conversion of grassland to arable land Changes in physical soil properties and in soil organic matter of the A-horizons due to the conversion of permanent grassland to arable land are quantified and described as a function of time for sandy soils. The study was carried out in an area northeast of Hannover. A decrease of about 100 t/ha C_org (- 57%), 5 – 6 t/ha N_org (- 58%) and 1 t/ha S_t (- 58%) was measured for a period of 2 – 4 years after grassland conversion. Thereby the quality of the soil organic matter remains unchanged (no changes of the C/N ratio and of the distribution of N_org in 5 N-fractions). However, an increase of soil bulk density from 1.0 to 1.3 g/cm³ and a decrease of total pore volume from 0.59 to 0.47 were observed. The fast mineralization of soil organic matter in the A-horizon following the conversion of grassland soils results in a temporary heavily increased nitrate input into the groundwater. Furthermore mineralization and leaching of nitrate and sulfate induces an acidification push in the soil by a proton release in the order of 350 keq/ha during a 2 – 4 years period. However, this proton production is compensated quantitatively by several applications of lime or marl by farmers and by the buffering of bases cations released from mineralized soil organic matter.  相似文献   

Nitrogen supply to cereals and sugar beet by mass flow and diffusion on a silty loam soil     

Otto Strebel  Wilhelmus H. M. Duynisveld 《植物养料与土壤学杂志》1989,152(2):135-141

In a four-year field study the nitrogen supply by mass flow and diffusion to cereals (spring wheat, winter barley, winter wheat) and sugar beet was investigated on a silty loam soil. The rates of water withdrawal, N mass flow and N diffusion were determined as a function of soil depth and time. The contribution to the N supply to roots by mass flow was 15–33% and mainly confined to the topsoil layer. The N supply by diffusion plays with 67–85% the dominant role, particularly in deeper rootzone layers. During periods of high N uptake, the N inflow (per unit root length and time) ranges between 0.26–2.07 μmol/(m · d) at various rootzone layers for cereal, and between 3.80–8.98 μmol/(m · d) for sugar beet, respectively. As a consequence of the high proportion of diffusion supply, at harvest the whole rootzone was largely depleted of nitrate. Thus, nitrate leaching losses during winter were small, the average nitrate concentration of the yearly groundwater recharge being only 7.9 mg N/l. Additionally, some results on supply of K, Ca, Mg and Cl for spring wheat and sugar beet are given. Diffusion supply prevails for K, and in the case of sugar beet for Mg and Cl also. Mass flow of Ca exceeded uptake considerably.  相似文献   

Ermittlung des Redoxpotentials (Eh-Wert) von Böden und Grundwässern aus dem zeitlichen Verlauf der Elektrodendepolarisation     

Jürgen Bttcher  Otto Strebel 《植物养料与土壤学杂志》1988,151(6):363-368

Calculation of redox potential in soil and groundwater from the curve of the electrode depolarization An inherent problem with redox potential measurements in soil and groundwater is the initial drift of potential readings. This is caused by electrode depolarization. The depolarization kinetics corresponds to a first-order process, mathematically described by an e-function. Based on the depolarization kinetics a method was developed to calculate redox potentials (E_h-values) from only short time (= 10 min) measured depolarization curves. Besides the E_h-value this procedure gives the depolarization constant λ. The method was tested and verified by a number of depolarization measurements in soils and groundwater.  相似文献   

Rotavirus infections in calves. 1. Adaptation of calf-pathogenic strains of rotavirus to cell culture     

P Otto  H Günther  P Heilmann 《Archiv fuer experimentelle veterinaermedizin》1986,40(4):605-620

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Studies of the spectrum of nonesterified fatty acids in blood and muscle tissue of swine. 1. Effect of genotype (muscular substance)     

V Mostschenko  E Otto 《Archiv fuer experimentelle veterinaermedizin》1979,33(5):717-724

The percentual composition of unesterified fatty acids in M. longissimus dorsi was determined by means of gas chromatography, and its correlations with the given genotype and pork condition were studied. Polyene fatty acids recorded from the Piétrain race deviated (C-18:2, C-18:3, C-20:4) from values recorded from large white and improved land race pigs. Animals of PSE nature were like Piétrain probands, in that their monoene acids were higher and diene acids lower by percentage than the comparable values in animals of normal pork condition.  相似文献   

Lysine requirement of fattening boars with reference to their performance. 4. Selected quantitative characteristics of the carcass and derivation of the lysine requirement     

G Michelchen  S Poppe  W Hackl  W Wiesmüller  E Otto 《Archives of Animal Nutrition》1981,31(7-8):513-518

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