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111.
V. G. Tumanyan Yu. A. Neyfack M. K. Pirtskhalava J. H. Männik 《Journal of biosciences》1985,8(3-4):593-602
On the basis of complete scanning through conformational space of dihedral angles, twelve structural genera were obtained.
Subsequent energy minimization within these genera yielded a limited set of duplexes with stacking: right-handed B-form (Wilkins
type), B2-form (Watson and Crick type) and left-handed Ll-form (Sasisekharan type) and the new L2-form. In the polymeric DNA
only right-handed double-helices are possible, the left-handed helices are forbidden due to poor 1–5 interchain contacts.
In contrast, for short fragments the left- and right-handed helicek have practically the same energies providing some physical
ground for side-by-side form, which biologically is possible as recombination form and may be as replication form. 相似文献
112.
元江干热河谷山地五百年来植被变迁探讨 总被引:15,自引:2,他引:13
元江河谷是云南省最干热地区之一,在海拔800—900米以下的山地上广泛分布着稀树灌草丛。根据《元江府志》(1714年编纂)、《元江州志》(1826年编纂)、《元江志稿》(1922年编篡)及对现存植被的考察,本文探讨了元江干热河谷山地五百年来植被的变迁。 元江县森林复盖率的减少与人口的增加有密切关系,十七世纪中期以前,森林复盖率在75%以上,十八、十九世纪时为70%左右,1958年为61.5%,1975年为27.3%,至1982年则为19.3%。研究表明,在十九世纪以前,这个地区分布的主要植被是热带季雨林,甚而热带季节雨林,以后热带稀树灌草丛则迅速发展。植被的历史变化与土壤流失密切相关。植物群落的演变是由以乔木树种为优势演变为以灌木种类为优势,再演变为以多年生草木植物为优势,而最后则成为裸地。本文也讨论了这个地区植被恢复的方法。 相似文献
113.
Summary Insight on the function of gangliosides. can emerge from knowledge of their cellular distribution. In this paper we review the structure of ganglioside GD3 and recent information on its cellular distribution. GD3 appears to be enriched in a variety of neural cell types including: reactive glia, gliomas, undifferentiated neurons, Muller glia, and oligodendroglia. Because each of these cell types share an enhanced permeability to ions and metabolites or possess properties associated with enhanced permeability, we suggest that GD3 is associated with enhanced membrane permeability. A possible function for GD3 in membrane permeability has implications for other cellular events such as metabolism, growth and interactions. 相似文献
114.
Characterization of purified cytochrome b-c1 complex from Rhodopseudomonas sphaeroides R-26 总被引:1,自引:0,他引:1
A highly purified cytochrome b-c1 complex from Rhodopseudomonas sphaeroides R-26 was isolated by a procedure involving Triton X-100 solubilization, calcium phosphate column chromatography, and ammonium sulfate fractionation. The purified enzyme complex contains, in nanomoles/mg of protein, cytochrome b, 8.3; cytochrome c1, 8.3; iron-sulfur protein, 15; phospholipids, 182; and ubiquinone, 5. Four major polypeptides with apparent molecular weights of 48,000, 30,000, 24,000, and 12,000 were detected in the sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The Mr = 48,000 and 30,000 proteins are cytochromes b and c1, respectively. The enzyme complex catalyzes electron transfer from ubiquinol to cytochrome c with a specific activity of 12.6 mumol of cytochrome c reduced per min/mg of protein at 23 degrees C. This is lower than that of the mitochondrial enzyme, although both systems have similar essential redox components and a similar Km for ubiquinol. The activity is fully sensitive to antimycin A and 5-n-undecyl-6-hydroxy-4, 7-dioxobenzothiazole. The enzyme complex is stable at neutral pH and at lower temperatures, but became less stable when the incubation temperature was raised. At 37 degrees C, the half-life is 15 min. The enzymatic activity was insensitive to treatment with N',N'-dicyclohexylcarbodiimide. No p-chloromercuriphenylsulfonate-alkylable sulfhydryl groups were detected. The major phospholipids associated with the purified enzyme complex are phosphatidylcholine, phosphatidylethanolamine, and phosphatidylglycerol with molar per cent distributions of 25, 21, and 35, respectively. About 60% of the enzymatic activity was abolished upon treatment with phospholipase A2. The phospholipase A2-inactivated activity can be partially restored by the addition of EDTA followed with phospholipids prepared from either the cytochrome b-c1 complex of the same source or a mixture of phosphatidylglycerol and asolectin.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
115.
Postsynaptic potentials produced by stimulating three sites of the midbrain superior colliculus were examined in motoneurons innervating the sternocleidomastoid, the trapezius, and the platysma cervical muscles in anesthetized cats. Stimulating the ipsilateral colliculus produced EPSP in the motoneurons as well as action potentials with a latency of 1.5–3.5 msec, averaging 2.6 ± 0.1 msec. Stimulation of the contralateral colliculus evoked EPSP with a latency of 1.5–3.2 msec and averaging 2.1 ± 0.1 msec together with IPSP with latency ranging from 2.6 to 5.0 msec. It is postulated that these postsynaptic responses are both monosynpatic and bisynaptic in nature. This type of synaptic action is assumed to be one of the mechanisms responsible for coordinated head movements produced by tectofugal impulses.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 2, pp. 197–202, March–April, 1986. 相似文献
116.
The effects of kainic acid on synaptic transmission in electroreceptors were investigated in the skate using techniques of uninterrupted superfusion of the synaptic area with a solution containing this substance and then recording the spike activity of single nerve fibers of the ampullae of Lorenzini. Kainic acid at threshold concentrations of the order of 10–9 M effectively changed spontaneous and evoked activity of the receptors. Level of background activity served as an indication of the effects taking place. During blockage of synaptic transmission produced by magnesium ions the addition of kainic acid to the magnesium-saturated solution restored both spontaneous and evoked activity. It was deduced that the action of kainic acid on skate electroreceptors is of a primarily presynaptic nature.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 18, No. 2, pp. 147–153, March–April, 1986. 相似文献
117.
K. E. Popov B. N. Smetanin V. S. Gurfinkel' M. P. Kudinova V. Yu. Shlykov 《Neurophysiology》1986,18(6):548-554
A study was made on normal human subjects, using a stabilograph to investigate changes in posture produced in response to transcutaneous galvanic stimulation of the right labyrinth. Results were obtained for different head positions and under the illusion of head and trunk rotation produced by stimulating (vibrating) the gulteus maximus muscle. In the absence of illusion of movement, the direction of the vestibulomotor response was determined by the position of the head in relation to the feed: with the normal head position, the body swayed on a frontal plane, and on a sagittal plane when the heat turned through 90°. Vestibulomotor responses were sagittally oriented, as with real head turning, when illusory head and trunk turning through 90° was produced by vibration. When the illusion of head rotation (in relation to the feet) was not produced by this stimulus, the direction of the postural response was not produced by this stimulus, the direction of the postural response was determined by the real orientation of the head. It is concluded that the spatial perception system plays a major part in controlling spatially oriented vestibulomotor responses.Institute for Research into Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 18, No. 6, pp. 779–787, November–December, 1986. 相似文献
118.
In somatic hybrids between tumourous Nicotiana tabacum (B6S3) and normal mesophyll Atropa belladonna cells, the following traits, directly or indirectly connected with T-DNA gene expression and tumourous growth, were analysed: lysopine dehydrogenase activity (LpDH), shoot suppression, root suppression, ability to grow on media with D-lactose as a sole carbon source and resistance to 2-aminoethylcysteine, 5-bromodeoxyuridine and 5-methyltryptophan. Dominant (semidominant) expression was observed for all but one trait studied, e.g. shoot suppression which behaved as a recessive character.Abbreviations LS-H
Linsmaier and Skoog (1965) hormone-free medium
- NAA
Naphtaleneacetic acid
- BAP
6-Benzylaminopurine
- 2,4-D
2,4-Dichlorophenoxyacetic acid
- 5-BUdR
5-Bromodeoxyuridine
- 2-AEC
2-Aminoethylcysteine
- 5-MT
5-Methyltryptophan 相似文献
119.
A general method for the synthesis of azido-ubiquinone derivatives has been developed directly by substituting one hydrogen atom on the benzoquinone ring with an azido group under weakly acidic conditions. The reaction takes several hours and the yield is generally low. The azido-ubiquinone was purified by preparative thin layer chromatography, and identified by NMR, IR and mass spectra. All the synthesized azido-ubiquinone derivatives show partial activity in mediating biological electron transfer in the dark, and show partial or complete inhibition upon photolysis. 相似文献
120.
The 13C-n.m.r. spectra of asialo-GM1 and GM1-oligosaccharide are completely assigned and compared to those previously found for intact GM1 and for the series GM4, GM3, GM2, GM1, GD1a, GD1b, and GT1b. Removal of the ceramide residue from GM1 liberated a free, reducing aldehyde group, which was reflected in a doubling of the 13C-n.m.r. signals assignable to the d-glucose residue because of α,β equilibrium. The spectrum of asialo-GM1 lacks the resonances from the sialic acid residue, as expected; in addition, several resonances from the neutral gangliotetraglycosyl residue shifted to different field positions after removal of sialic acid from GM1. These resonances include that of C-4 of the inner β-d-galactosyl residue, and C-1 of the 2-acetamido-2-deoxy-d-galactosyl residue that is near the site of attachment of the sialosyl residue. The differences between the chemical shifts of the carbon resonances of oligomeric and monomeric saccharides, termed linkage shifts, provide a quantitative assignment aid. They are ~ of those for residues linked to sialic acid than those for residues linked to the neutral hexose chain. Correlations among linkage shifts for pairs of glycosidically-linked carbon atoms for asialo-GM1 and GM1-oligosaccharide were compared with those for the series of gangliosides GM4 to GT1b, and differences are noted for resonances for carbon atoms near the sialic acid residue. The spectrum of ganglioside GM1b, a positional isomer of GM1 whose 13C-n.m.r. spectrum has not yet been observed, is predicted. 相似文献