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51.
Summary A 3D1H–15N–13C triple resonance experiment is presented that contains exclusively cross peaks between the1HN and15N nuclei of one residue with the H of the preceding residue. The pulse sequence, designed to minimize the time coherence, is transverse on nuclei with short T2 values. The experiment consists of coherence transfers via one-bond couplings from the HN via N, CO, C to the H and back to the HN for detection; it is called HN(COCA)HA. The experiment was tested on uniformly15N- and13C-enriched T4 lysozyme. 相似文献
52.
High-resolution proton magnetic resonance spectroscopy was used to analyze human cerebrospinal fluid obtained from patients with several neurological problems. The major metabolites measured included glucose, lactate, glutamine, citrate, inositol, acetate, creatine, creatinine, beta-hydroxybutyrate, alanine, and pyruvate. A drug vehicle, propylene glycol, was also measured. Alterations in the cerebrospinal fluid of these metabolites provided information concerning metabolism of the brain. Magnetic resonance spectroscopy offered a simple and rapid means of assessing these and other exogenous and endogenous compounds in diseases affecting the nervous system. 相似文献
53.
Genetic reconstruction and functional analysis of the repeating lipoyl domains in the pyruvate dehydrogenase multienzyme complex of Escherichia coli 总被引:11,自引:0,他引:11
J R Guest H M Lewis L D Graham L C Packman R N Perham 《Journal of molecular biology》1985,185(4):743-754
The dihydrolipoamide acetyltransferase component (E2p) of the pyruvate dehydrogenase complex of Escherichia coli contains three highly homologous sequences of about 100 residues that are tandemly repeated to form the N-terminal half of the polypeptide chain. All three sequences include a lysine residue that is a site for lipoylation and they appear to form independently folded functional domains. These lipoyl domains are in turn linked to a much larger (about 300 residues) subunit-binding domain of the E2p chain that aggregates to form the octahedral inner core of the complex and also contains the acetyltransferase active site. In order to investigate whether individual lipoyl domains play different parts in the enzymic mechanism, selective deletions were made in vitro in the dihydrolipoamide acetyltransferase gene (aceF) so as to excise one or two of the repeating sequences. This was facilitated by the high degree of homology in these sequences, which allowed the creation of hybrid lipoyl domains that closely resemble the originals. Pyruvate dehydrogenase complexes incorporating these genetically reconstructed E2p components were purified and their structures were confirmed. It was found that the overall catalytic activity, the system of active site coupling, and the ability to complement pyruvate dehydrogenase complex mutants, were not significantly affected by the loss of one or even two lipoyl domains per E2p chain. No special role can be attached thus far to individual lipoyl domains. On the other hand, certain genetic deletions affecting the acetyltransferase domain caused inactivation of the complex, highlighting particularly sensitive areas of that part of the E2p chain. 相似文献
54.
Annette Gulik Vittorio Luzzati Mario De Rosa Agata Gambacorta 《Journal of molecular biology》1985,182(1):131-149
We describe in this work the structure and polymorphism of a variety of lipids extracted from Sulfolobus solfataricus, an extreme thermoacidophilic archaebacterium growing at about 85 °C and pH 2. These lipids are quite different from the usual fatty acid lipids of eukaryotes and prokaryotes: each molecule consists of two C40 ω-ω′ biphytanyl residues (with 0 to 4 cyclopentane groups per residue), ether linked at both ends to two (variably substituted) glycerol or nonitol groups. Four lipid preparations were studied; the total and the polar lipid extracts, and two hydrolytic fractions, the symmetric glycerol dialkyl glycerol tetraether and the asymmetric glycerol dialkyl nonitol tetraether, as a function of water content and temperature, using X-ray scattering techniques. The main conclusions from the study of the four lipid preparations can be summarized as follows. (1) As with other lipids, a remarkable number and variety of phases are observed over a temperature-concentration range close to “physiological” conditions. The possibility is discussed that this polymorphism reflects a fundamental property of lipids, closely related to their physiological rôle. (2) As in other lipids, two types of chain conformations are observed: a disordered one (type α) at high temperature; at lower temperature, a more ordered packing of stiff chains, all parallel to each other (type β′). At temperatures and degrees of hydration approaching the conditions prevailing in the living cell, the conformation is of type α. (3) In all the phases with chains in the α conformation, the unsubstituted glycerol headgroups, whose concentration is high in these lipids, segregate in the hydrocarbon matrix, away from the other polar groups. This property may have interesting biological consequences: for example, the chains of a fraction of the bipolar lipid molecules can span hydrocarbon gaps as wide as 75 Å. (4) Two cubic phases are observed in the total and the polar lipid extracts, which display a remarkable degree of metastability, most unusual in lipid phase transitions involving structures with chains in the α conformation. This phenomenon can be explained by the interplay of the physical structure of the cubic phases (the two contain two intertwined and unconnected three-dimensional networks of rods) and the chemical structure of the lipid molecules: the two headgroups of most molecules being anchored on each of the two networks of rods, the migration of the lipid molecules is hindered by the two independent diffusion processes and by the entanglement of the chains. The possibility is discussed that this phenomenon may reflect an evolutionary response to a challenge of the natural habitat of these archaebacteria. 相似文献
55.
Summary A model has been developed for 5-nitroxide stearate, I(12,3), distribution in human erythrocyte ghosts which accurately predicts ESR spectral alterations observed with increased probe/total lipid (P/L) at 37°C. This spin probe occupies a class of high-affinity, noninteracting sites at low loading. Saturation occurs with increasing probe concentration, and, at higher loading, the probe inserts itself at initially dilute sites to form membranebound clusters of variable size. No low probe remains at high P/L where all I(12,3) clusters in a concentrated phase. This model allows determination of the dilute/clustered probe ratio, and shows that I(12,3) segregates in erythrocytes at what might otherwise be considered low P/L (e.g., 1/359). These findings validate the earlier use of empirical parameters to estimate probe sequestration in biological membranes. 相似文献
56.
David A. Priestley Brenda G. Werner A. Carl Leopold Murray B. McBride 《Physiologia plantarum》1985,64(1):88-94
In view of their possible role in oxidative deterioration of seeds and pollen, organic free radicals were measured by electron spin resonance in embryonic axes and cotyledons of soybean [ Glycine max (L.) Merr], embryo and endosperm fractions of corn [ Zea mays L.] and pollen of cattail [ Typha latifolia L.]. A pronounced decline in the radical signal ensued when hydration increased above about 7% (wet weight basis) in both the seed materials and in pollen. Moderate hydration of the soybean axis followed by drying led to a small decrease in organic free radicals compared to untreated material, especially if the desiccation step was performed under nitrogen. In a comparison of soybeans of various ages under normal storage, organic free radical levels in the axis showed little or no increase with age. In marked contrast, over 5 days of accelerated aging at 40°C and near-saturating humidity, organic radical levels approximately doubled in the axis. This pronounced increase in free radical content was not associated with a decrease in the proportion of polyunsaturated fatty acids. The data suggest that hydration of seed and pollen causes a release of free radicals from the trapped state. 相似文献
57.
Milan Höfer Klaas Nicolay George Robillard 《Journal of bioenergetics and biomembranes》1985,17(3):175-182
The electrochemical gradient of protons,
, was estimated in the obligatory aerobic yeastRhodotorula glutinis in the pH0 range from 3 to 8.5. The membrane potential, , was measured by steady-state distribution of the hydrophobic ions, tetraphenylphosphonium (TPP+) for negative above pH0 4.5, and thiocyanate (SCN–) for positive below pH0 4.5. The chemical gradient of H+ was determined by measuring the chemical shift of intracellular Pi by31P-NMR at given pH0 values. The values of pHi increased almost linearly from 7.3 at pH0 3 to 7.8 at pH0 8.5. In the physiological pH0 range from 3.5 to 6,
was fairly constant at values between 17–18 KJ mol–1, gradually decreasing at pH0 above 6. In deenergized cells, the intracellular pHi decreased to values as low as 6, regardless of whether the cell suspension was buffered at pH0 4.5 or 7.5. There was no membrane potential detectable in deenergized cells. 相似文献
58.
K. D. Hahn F. Buck H. Rüterjans B. K. Chernov K. G. Skryabin M. P. Kirpichnikov 《European biophysics journal : EBJ》1985,12(2):87-95
The 17 base pair operator O
R
3 oligonucleotide, which is the preferential binding site for the Cro repressor of phage , was studied by two-dimensional NMR spectroscopy. A sequential assignment procedure based on two-dimensional Nuclear Overhauser Effect (NOESY) and scalar coupling correlated (COSY) NMR spectroscopy, together with the knowledge of the oligodesoxynucleotide sequence, made it possible to assign the non-exhangeable base protons and the H1 and the H2-H2 sugar protons of the O
R
3 operator DNA. The pattern of the observed NOE connectivities is consistent with a right-handed helical DNA structure. The base and sugar proton assignments provide the necessary information for further studies of the O
R
3 operator — Cro repressor interaction.Abbreviations COSY
correlated spectroscopy
- FID
free induction decay
- NOE
nuclear Overhauser effect
- NOESY
nuclear Overhauser effect spectroscopy
- RD
relaxation delay
- TSP
sodium 3-trimethylsilyl-(2,2,3,3-2H4)propionate
- EDTA
sodium ethylendiamine tetraacetate 相似文献
59.
The X-ray structure determination of yeast phosphoglycerate kinase and subsequent substrate binding studies have helped to
define the binding sites for the triose and nucleoside phosphate substrates. This communication deals with one feature of
the binding site—the location of an aspartic acid residue close to the phosphoryl binding site of the nucleotide substrate—and
relates this and other structural features of the active site to the properties of this enzyme as deduced from nuclear magnetic
resonance studies. 相似文献
60.
A. Birkenfeld M. Weber-Benndorf Prof. Dr. Dr. H. M. Beier 《Cell and tissue research》1985,239(3):497-503
Summary The effect of clomiphene citrate on the rabbit ovary was studied in mature nulliparous rabbits pretreated with three consecutive doses ranging from 0.01–10.0 mg/kg per day. With increasing doses a trend of decrease in mean ovarian weight (mg/kg body weight) is observed 2 days after termination of treatment. Five days later a significant increase occurs, which then subsides again to control values on day 12 after termination of treatment. During this period, no matings or injections of luteinizing hormone were performed to trigger ovulation; consequently no ovulations are observed. Folliculogenesis appears as normally; number and morphology of follicles are within normal ranges. No endogenous, spontaneous gonadotropin surges are detected in blood serum up to the 7th day after termination of treatment (2 and 10 mg doses). The surface epithelium of the ovary resembles normal germinal epithelium; however, after treatment with high doses a secretory-like activity is observed, accompanied with ultrastructural changes.Supported by the Deutsche Forschungsgemeinschaft, Special Program on Biology and Clinics of Reproduction. (Grant Be 524/7-7).Visiting Scientist from the Department of Obstetrics and Gynecology, Hadassah University Hospital, Jerusalem, Israel. 相似文献