The influence of spermine on the structural dynamics of yeast tRNA

A tRNA^Phe derivative carrying ethidium at position 37 in the anticodon loop has been used to study the effect of spermine on conformational transitions of the tRNA. As previously reported (Ehrenberg, M., Rigler, R. and Wintermeyer, W. (1979) Biochemistry 18, 4588–4599) in the tRNA derivative the ethidium is present in three states (T₁–T₃) characterized by different fluorescence decay rates. T-jump experiments show two transitions between the states, a fast one (relaxation time 10–100 ms) between T₁ and T₂, and a slow one (100–1000 ms) between T₂ and T₃. In the presence of spermine the fast transition shows a negative temperature coefficient indicating the existence of a preequilibrium with a negative reaction enthalpy. Spermine shifts the distribution of states towards T₃, as does Mg²⁺, but the final ratio obtained with spermine is higher than with Mg²⁺, which we tentatively interpret to mean that spermine stabilizes one particular conformation of the anticodon loop.     

The influence of spermine on the structural dynamics of yeast tRNAPhe

A tRNA^Phe derivative carrying ethidium at position 37 in the anticodon loop has been used to study the effect of spermine on conformational transitions of the tRNA. As previously reported (Ehrenberg, M., Rigler, R. and Wintermeyer, W. (1979) Biochemistry 18, 4588–4599) in the tRNA derivative the ethidium is present in three states (T₁–T₃) characterized by different fluorescence decay rates. T-jump experiments show two transitions between the states, a fast one (relaxation time 10–100 ms) between T₁ and T₂, and a slow one (100–1000 ms) between T₂ and T₃. In the presence of spermine the fast transition shows a negative temperature coefficient indicating the existence of a preequilibrium with a negative reaction enthalpy. Spermine shifts the distribution of states towards T₃, as does Mg²⁺, but the final ratio $\text{[}\text{T}{}_2\text{]}\text{[}\text{T}{}_1\text{]}$ obtained with spermine is higher than with Mg²⁺, which we tentatively interpret to mean that spermine stabilizes one particular conformation of the anticodon loop.     

经济管理向生态经济管理的转变

在现代社会中,人类的经济建设以与自然过程相竞争的规模进行着,所造成的生态影响不仅表现在地区生态系统的结构和功能上,也表现在生物圈中,而且还从地球化学循环中显示出来。这种情况,使得现代社会的经济管理,必然由传统的经济管理逐步转变成生态经济管理。     

The meaning of interaction parameters in two-state protein complexes

The theory of interaction parameters has thus far been based on the free-energy relationships in the formation of ternary complexes formed between a pair of ligands and a protein molecule. The concept has been formulted in terms of a thermodynamic square comprised of the free protein, the two binary complexes, and the ternary complex. However, an increasing number of proteins have been found to exist as equilibrium mixtures of two macrostates. The equilibrium constants for such two-state transitions vary quite considerably between the various binary and ternary complexes of a given protein. We show here that the interpretations of interaction parameters in such two-state systems, requiring the use of a thermodynamic cube, are much more complex than those based on the classic thermodynamic square commonly employed. We demonstrate the use of enthalpies of interaction and heat capacities of interaction to analyze the source of observed free enerigies of interaction in such systems. Specifically, we find that measured negative interaction parameters may arise simply from the inability of a system to achieve all of the positive component effects anticipated by the conventional formulation.     

Import of 14C-Photosynthate by Developing Leaves of Sugarcane

Sink-to-source transition was studied in developing sugarcane (Saccharum interspecific variety L62–96) leaves. Fully-expanded, mature sugarcane leaves were fed ¹⁴CO₂ for 20 minutes, incorporating about 617 Bq. After five hours the leaves of each plant were cut into 1-cm-length segments that were weighed and then placed in scintillation cocktail for counting. All leaves younger than the leaf fed ¹⁴CO₂ imported labeled photoassimilate. Three to four leaves had both importing and non-importing regions within the blade and a distinct transition region between them. A transition region was observed in leaves which had expanded to between 30 and 90 % of final blade length. Radioactivity per gram fresh weight was calculated as a measure of sink strength. Sink strength was greatest in the youngest leaf and declined with leaf age. The results of this study indicate that 1) import of photosynthate by developing sugarcane leaves occurs over a longer span of developmental ages than in dicotyledonous leaves and 2) the actual tissue region undergoing transition within such a leaf can be resolved as narrow zone between the importing and non-importing regions.     

A new species of Macrothrix (Anomopoda: Macrothricidae) from Central Mexico

Macrothrix mexicanus sp. nov. is described from central México, a transition zone between the nearctic and neotropics. All localities where it was found are over 1800 meters above sea level. It shows many resemblances with M. laticornis, M. camjatae and M. rosea but is characterized by a persistent dorsal tooth on the valve keel, a spinous papilla on the basipodite of the antenna, the second thoracic limb with a long conical sensillum between scraper 1 and the gnathobase, the endopod of trunk limb IV having two setae; the postabdomen with the dorsal margin bilobed, and the distal segment of the seta natatoria which is unusually long.Abbreviations used on figures EN Endopodite - EP Epipodite - EX Exopodite - IDL Inner distal lobe - ODL Outer distal lobe - GT Gnatobase - E1 Endite 1 - E2 Endite 2 - E3 Endite 3     

Control of Photosystem II in spinach leaves by continuous light and by light pulses given in the dark

The light-induced induction of components of non-photochemical quenching of chlorophyll fluorescence which are distinguished by different rates of dark relaxation (qNf, rapidly relaxing and qNs, slowly relaxing or not relaxing at all in the presence brief saturating light pulses which interrupt darkness at low frequencies) was studied in leaves of spinach.After dark adaptation of the leaves, a fast relaxing component developed in low light only after a lag phase. Quenching increased towards a maximum with increasing photon flux density. This fast component of quenching was identified as energy-dependent quenching qE. It required formation of an appreciable transthylakoid pH and was insignificant when darkened spinach leaves received 1 s pulses of light every 30 s even though zeaxanthin was formed from violaxanthin under these conditions.Another quenching component termed qNs developed in low light without a lag phase. It was not dependent on a transthylakoid pH gradient, decayed exponentially with a long half time of relaxation and was about 20% of total quenching irrespective of light intensity. When darkened leaves were flashed at frequencies higher than 0.004 Hz with 1 s light pulses, this quenching also appeared. Its extent was very considerable, and it did not require formation of zeaxanthin. Relaxation was accelerated by far-red light, and this acceleration was abolished by NaF.We suggest that qNs is the result of a so-called state transition, in which LHC II moves after its phosphorylation from fluorescent PS II to nonfluorescent PS I. This state transition was capable of decreasing in darkened leaves the potential maximum quantum efficiency of electron flow through Photosystem II by about 20%.Abbreviations PFD photon flux density - PS photosystem     

中国典型草原放牧草场蝗虫为害损失及经济阈值的估算(英语)

传统上估算蝗虫在放牧草场为害损失的方法几乎都是用来测定对牧草秋季产量的影响,而实际上,在估算放牧草场蝗虫为害损失及经济阈值时,牧草的现存量而非秋季产量是更应考虑的因素.本文提出了一种适合测定蝗虫对牧草现存生物量影响的新方法,即野外挂笼饲养与蝗虫种群动态相结合的估算方法,并在此基础上组建了放牧草场蝗虫种群经济阈值模型;α_0 α_1M_1_α_2M_2_ α_3S_1 α_4S_2=C其中,M_1:狭翅雏蝗生物量;M_2:宽须蚁蝗生物量;S_1:狭翅雏蝗平均个体重量,S_2:宽须蚁蝗平均个体重量;α_0-α_4:常数.同时引入蝗虫种群数量和生物量两项参数来表达蝗虫种群的发生程度.     

Inhibition of the mitochondrial Ca2+ uniporter by pure and impure ruthenium red

Commercial ruthenium red is often purified by a single recrystallization as described by Luft, J.H. (1971) Anat Rec 171, 347–368, which yields small amounts of material having an apparent molar extinction coefficient of 67,400 at 533 nm. A simple modification to the procedure dramatically improves the yield, allowing crystallization to be repeated. Three times recrystallized ruthenium red has an apparent extinction coefficient of 85,900, the highest value reported to date. Both crude and highly purified ruthenium red can be shown to inhibit reverse activity of the mitochondrial Ca²⁺ uniporter (uncoupled mitochondria), provided that care is taken to minimize and account for Ca²⁺ release through the permeability transition pore. Crude ruthenium red is 7–10 fold more potent than the highly purified material in this regard, on an actual ruthenium red concentration basis. The same relative potency is seen against forward uniport (coupled mitochondria), however, the I₅₀ values are 10 fold lower for both the crude and purified preparations. These data demonstrate unambiguously that the energy state of mitochondria affects the sensitivity of the Ca²⁺ uniporter to ruthenium red preparations, and that both the forward and reverse reactions are subject to complete inhibition. The data suggest, however, that the active inhibitor may not be ruthenium redper se, but one or more of the other ruthenium complexes which are present in ruthenium red preparations.Abbreviations CCP carbonyl cyanide p-chlorophenylhydrazone - CSA cyclosporin A - Hepes 4-(2-hydroxyethyl)-1-piperazine ethanesulfonic acid