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1.
Md. Khurshid Alam Khan Md. Hamidur Rahaman Md. Imtaiyaz Hassan Tej P. Singh Ali A. Moosavi-Movahedi Faizan Ahmad 《Journal of biological inorganic chemistry》2010,15(8):1319-1329
It has already been shown that the mutant Leu94Gly of horse cytochrome c exists in a molten globule (MG) state. We have carried out studies of reversible folding and unfolding induced by LiCl of
this mutant at pH 6.0 and 25 °C by observing changes in the difference molar absorption coefficient at 402 nm, the mean residue
ellipticity at 222 nm, and the difference mean residue ellipticity at 409 nm. This process is a three-state process when measured
by these probes. The stable folding intermediate state has been characterized by far- and near-UV circular dichroism, tryptophan
fluorescence, 8-anilino-1-naphthalenesulfonic acid binding, and dynamic light scattering measurements, which led us to conclude
that the intermediate is a premolten globule (PMG). Analysis of the reversible unfolding transition curves for the stability
of different states in terms of the Gibbs free energy change at pH 6.0 and 25 °C led us to conclude that the MG state is more
stable than the PMG state by 5.4 ± 0.1 kcal mol−1, whereas the PMG state is more stable than the denatured (D) state by only 1.1 ± 0.1 kcal mol−1. A comparison of the conformational and thermodynamic properties of the LiCl-induced PMG state at pH 6.0 with those of the
PMG state induced by NaCl at pH 2.0 suggests that a similar PMG state is obtained under both denaturing conditions. Differential
scanning calorimetry measurements suggest that heat induces a reversible two-state transition between MG and D states. 相似文献
2.
Calcareous nannofossils originated in the Triassic, radiated in the Jurassic and became a dominant component of the marine
biosphere from the earliest Jurassic onward. They can be considered as one of the most important “innovations” of the Mesozoic
oceans. Their basic morphology allows the differentiation of three different groups: coccoliths, nannoliths and calcispheres
(= calcareous dinocysts). Only coccoliths and nannoliths are discussed in this article in some detail. Coccoliths and nannoliths
have contributed greatly in the Interpretation of Mesozoic marine Systems through biostratigraphy and palaeoecology/palaeoceanography.
Ever since the late 1960s both coccoliths and nannoliths have proven to be useful and reliable zonal markers for biostratigraphic
schemes, allowing detailed zonations for the Jurassic and Cretaceous. Though affected by palaeobiogeographic provincialism,
coccoliths and nannoliths have supplied many cosmopolitan biostratigraphic markers. These allow a global correlation of marine
sedimentary units both from onshore sections in the classical European and North American areas and pelagic sequences recovered
in the course of the DSDP/ODP drilling from the world’s oceans. Thus research on calcareous nannofossils Covers both, regional
and global aspects. Research in the last 15 years concentrated on palaeoecological aspects. Apart from dinoflagellates, coccolithophores
were the most important primary producers in Mesozoic oceans. As such they heavily relied on autecological factors such as
light, nutrients and temperature. Variations in the assemblage composition of these groups may thus be viewed as a key for
understanding palaeoecological, palaeoceanographic and palaeoclimatic changes of the past.
相似文献
3.
Solving the protein folding problem is one of the most challenging tasks in the post genomic era. Identification of folding-initiation sites is very important in order to understand the protein folding mechanism. Detection of residual structure in unfolded proteins can yield important clues to the initiation sites in protein folding. A substantial number of studied proteins possess residual structure in hydrophobic regions clustered together in the protein core. These stable structures can work as seeds in the folding process. In addition, local preferences for secondary structure in the form of turns for beta-sheet initiation and helical turns for alpha-helix formation can guide the folding reaction. In this respect the unfolded states, studied at increasing structural resolution, can be the Rosetta Stone of the protein folding problem. 相似文献
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Relation between the oxidation state of nicotinamide–adenine dinucleotide and the metabolism of spermatozoa
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1. The existing procedures for extraction of oxidized and reduced nicotinamide coenzymes were adapted to spermatozoa to overcome the coenzyme-degrading activity of seminal plasma. 2. The content of total NAD(+) and NADH was determined in the spermatozoa of ram, bull, boar, stallion and cock. NADP(+) and NADPH were not detected in ram spermatozoa. 3. The oxidation state of sperm NAD depended on the seminal plasma, the removal of which produced a change in the percentage oxidation state of the coenzyme, 100x[NAD(+)/(NAD(+)+NADH)], without altering the total content of NAD(+)+NADH. 4. In suspensions of washed ram spermatozoa, incubated anaerobically at 25 degrees C, the percentage oxidation state of NAD declined with increasing spermatozoa concentration. 5. When ram or boar spermatozoa that had been previously washed and resuspended in Ringer phosphate medium, were incubated anaerobically at 25 degrees C with various substances, pronounced effects on the percentage oxidation state of NAD could be observed with l-lactate, pyruvate, oxaloacetate, dihydroxyacetone, formaldehyde and glyceraldehyde; sorbitol and acetoacetate acted only on ram spermatozoa; fructose, glucose, mannose and acetaldehyde acted predominantly on boar spermatozoa. Formaldehyde lowered the (NAD(+)+NADH) content of ram spermatozoa, but none of the other substances had a comparable effect. 6. The percentage oxidation state of sperm NAD was not influenced by exogenous cysteine, cystine, ergothioneine or ascorbate. 7. A highly active sorbitol dehydrogenase could be prepared from ram, but not from boar, spermatozoa. 8. Sorbitol, acetoacetate and 3-hydroxybutyrate effectively supported the respiration of ram, but not boar, spermatozoa. 9. ;Cold shock', resulting from sudden cooling of spermatozoa, abolished motility completely and irreversibly but produced only a slow and partial decrease in the total NAD content. Slight over-heating, sufficient to produce loss of motility, had no adverse effect on the total NAD content. 10. Storage of ram sperm at 14 degrees C produced only a small decrease of NAD after 2 days, but subsequently the loss became greater. 相似文献
7.
Biodiesel production—current state of the art and challenges 总被引:3,自引:0,他引:3
Biodiesel is a clean-burning fuel produced from grease, vegetable oils, or animal fats. Biodiesel is produced by transesterification
of oils with short-chain alcohols or by the esterification of fatty acids. The transesterification reaction consists of transforming
triglycerides into fatty acid alkyl esters, in the presence of an alcohol, such as methanol or ethanol, and a catalyst, such
as an alkali or acid, with glycerol as a byproduct. Because of diminishing petroleum reserves and the deleterious environmental
consequences of exhaust gases from petroleum diesel, biodiesel has attracted attention during the past few years as a renewable
and environmentally friendly fuel. Since biodiesel is made entirely from vegetable oil or animal fats, it is renewable and
biodegradable. The majority of biodiesel today is produced by alkali-catalyzed transesterification with methanol, which results
in a relatively short reaction time. However, the vegetable oil and alcohol must be substantially anhydrous and have a low
free fatty acid content, because the presence of water or free fatty acid or both promotes soap formation. In this article,
we examine different biodiesel sources (edible and nonedible), virgin oil versus waste oil, algae-based biodiesel that is
gaining increasing importance, role of different catalysts including enzyme catalysts, and the current state-of-the-art in
biodiesel production.
JIMB 2008: BioEnergy—special issue. 相似文献
8.
Szmitko PE Teoh H Stewart DJ Verma S 《American journal of physiology. Heart and circulatory physiology》2007,292(4):H1655-H1663
The cardiometabolic syndrome, associated with increased cardiovascular disease risk in the industrialized world, is estimated to affect one in four adults. Although the mechanisms linking obesity and cardiovascular disease remain unclear, research continues to unravel the molecular pathways behind this pandemic. Adipose tissue has emerged as a metabolically active participant in mediating vascular complications, serving as an active endocrine and paracrine organ secreting adipokines, which participate in diverse metabolic processes. Among these adipokines is adiponectin, which seems to possess antiatherogenic and anti-inflammatory effects and may be protective against cardiovascular disease development. The current review describes the pathophysiology of adiponectin in atherosclerotic disease. 相似文献
9.
Interplay between proteins, nucleic acids, carbohydrates and/or lipids is involved in almost every process in life on earth.
As a consequence, a wide range of diseases results from abnormal interactions of such biomolecules. The main motivation of
foldamer science is the development of scaffolds that are capable of adopting defined structures, mimicking parts of biological
protagonists in their function. Among the most fundamental interactions in living beings are those between proteins, the so
called protein–protein interactions (PPIs). Therefore, peptidic foldamers bear the promise to be an important tool for the
inhibition of PPIs, as they are structurally most similar to the original proteins. The great number of possible permutations
given by the combination of proteinogenic α-amino acid residues along with β-amino acids opens the door for a larger pool
of accessible structures with potential applications. Despite the increasing amount of new secondary structure motifs, only
few examples for tertiary and quaternary structure design, as well as inhibition of PPIs, have been realized so far. In this
review, we summarize the current knowledge and recent progress made in the field of α/β-peptide foldamers beginning from secondary
structure design up to highly sophisticated biological applications, such as protein surface recognition and inhibition of
HIV cell entry. 相似文献
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Prolonged morphine treatment induces extensive desensitization of the μ-opioid receptor (μOR) which is the G-protein-coupled receptor that primarily mediates the cellular response to morphine. To date, the molecular mechanism underlying this process is unknown. Here, we have used live cell fluorescence imaging to investigate whether prolonged morphine treatment affects the physical environment of μOR, or its coupling with G-proteins, in two neuronal cell lines. We find that chronic morphine treatment does not change the amount of enhanced yellow fluorescence protein (eYFP)-tagged μOR on the plasma membrane, and only slightly decreases its association with G-protein subunits. Additionally, morphine treatment does not have a detectable effect on the diffusion coefficient of eYFP-μOR. However, in the presence of another family member, the δ-opioid receptor (δOR), prolonged morphine exposure results in a significant increase in the diffusion rate of μOR. Number and brightness measurements suggest that μOR exists primarily as a dimer that will oligomerize with δOR into tetramers, and morphine promotes the dissociation of these tetramers. To provide a plausible structural context to these data, we used homology modeling techniques to generate putative configurations of μOR-δOR tetramers. Overall, our studies provide a possible rationale for morphine sensitivity. 相似文献
13.
Control of the redox state of the nicotinamide–adenine dinucleotide couple in rat liver cytoplasm 总被引:1,自引:0,他引:1
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1. A study has been made of the ability of rat liver in vivo to maintain equilibrium in the combined glyceraldehyde 3-phosphate dehydrogenase, 3-phosphoglycerate kinase and lactate dehydrogenase reactions, i.e. in the system: [Formula: see text] Attempts were made to upset equilibrium. The [lactate]/[pyruvate] ratio was rapidly changed by injection of ethanol or crotyl alcohol, and the value of [ATP]/[ADP][HPO(4) (2-)] was rapidly changed by injection of ethionine or carbonyl cyanide p-trifluoromethoxy-phenylhydrazone. 2. The concentrations of the metabolites occurring in the above equation were measured in freeze-clamped liver. 3. Although the injected agents caused large changes in the concentrations of the individual components, near-equilibrium in the system was maintained, as indicated by the fact that the value of [ATP]/[ADP][HPO(4) (2-)], referred to as the phosphorylation state of the adenine nucleotides, measured directly agreed with the value calculated for equilibrium conditions from the above equation. 4. The results are discussed and taken to confirm that the order of magnitude of the value of the redox state of the cytoplasmic NAD couple in rat liver is controlled by the phosphorylation state of the adenine nucleotide system. 相似文献
14.
《BBA》2006,1757(9-10):1073-1083
Mitochondrial Complex II (succinate:ubiquinone oxidoreductase) is purified in a partially inactivated state, which can be activated by removal of tightly bound oxaloacetate (E.B. Kearney, et al., Biochem. Biophys. Res. Commun. 49 1115–1121). We crystallized Complex II in the presence of oxaloacetate or with the endogenous inhibitor bound. The structure showed a ligand essentially identical to the “malate-like intermediate” found in Shewanella Flavocytochrome c crystallized with fumarate (P. Taylor, et al., Nat. Struct. Biol. 6 1108–1112) Crystallization of Complex II in the presence of excess fumarate also gave the malate-like intermediate or a mixture of that and fumarate at the active site. In order to more conveniently monitor the occupation state of the dicarboxylate site, we are developing a library of UV/Vis spectral effects induced by binding different ligands to the site. Treatment with fumarate results in rapid development of the fumarate difference spectrum and then a very slow conversion into a species spectrally similar to the OAA-liganded complex. Complex II is known to be capable of oxidizing malate to the enol form of oxaloacetate (Y.O. Belikova, et al., Biochim. Biophys. Acta 936 1–9). The observations above suggest it may also be capable of interconverting fumarate and malate. It may be useful for understanding the mechanism and regulation of the enzyme to identify the malate-like intermediate and its pathway of formation from oxaloacetate or fumarate. 相似文献
15.
AIMS: To investigate whether modifications in Yersinia pestis isolates from three plague foci from the state of Ceará, Brazil, had occurred over the years as a consequence of genetic adaptation to the environment. METHODS AND RESULTS: The isolates were studied with respect to susceptibility to antimicrobial drugs, plasmid and protein profiling, pigmentation on Congo red-agar plates, and the presence of some pathogenicity genes using PCR. Most of the expected virulence markers were detected in the cultures examined. There was no evidence of any alteration that could be associated with their origin (patients, rodents and fleas) or period of isolation (1971-1997). CONCLUSIONS, SIGNIFICANCE AND IMPACT OF THE STUDY: Phenotypic or genotypic changes were not detected in the cultures examined. However, the results obtained will serve as a reference to follow the evolution of Y. pestis in these foci. 相似文献
16.
Background
The use of targeted LC-MS/MS methods for protein quantitation in clinical laboratories implies a careful evaluation of potential sources of analytical interference. In this study, we investigated whether inflammation, which is associated with both the release of proteolytic enzymes and increased expression of acute phase protease inhibitors, is affecting the accuracy of a haptoglobin selected reaction monitoring (SRM) assay.Results
A SRM assay was developed and used to quantify haptoglobin in 57 human serum samples. The SRM assay had CVs (n = 6) of 12.9% at 698 mg/L and 11.8% at 1690 mg/L. Results of the SRM assay were compared to those of a commercial immunonephelometric test. Passing-Bablok regression gave a proportional bias of 0.92 (95% CI: 0.82 to 1.04) and a constant bias of 75.40 (95% CI: −71.09 to 251.04), indicating that SRM and immunonephelometric assays provided comparable results. We then investigated whether the accuracy of the SRM assay was influenced by the patient’s inflammatory state by assessing the relationship between the serum CRP concentration and the bias between the two methods. No correlation was found between the SRM/immunoassay bias and the CRP concentration (Pearson correlation coefficient r = 0.0898).Conclusions
These data indicate that neither the release of proteolytic enzymes nor the increased level of protease inhibitors occurring during inflammation processes have a significant impact on the haptoglobin SRM assay accuracy. Such studies provide important information about potential sources of analytical interferences in protein SRM assays.Electronic supplementary material
The online version of this article (doi:10.1186/1559-0275-11-38) contains supplementary material, which is available to authorized users. 相似文献17.
In 1989–2005 the qualitative composition and seasonal and inter-annual dynamics of the total biomass of phytoplankton, chlorophyll
a content, hydrological, and hydrochemical parameters were studied in the Russian zone of the Vistula Lagoon in the Baltic
Sea. The results of these observations were compared to the data obtained in the 1950s and 1970s. The structural reorganization
of phytoplankton was revealed, testifying to the negative changes in the ecosystem under conditions of anthropogenic pollution
and eutrophication, climate warming, and increasing salinity. 相似文献
18.
Binding of 8-anilino-1-naphthalene sulphonate (ANS) to rat liver mitochondria and submitochondrial inside-out particles was measured under energized and de-energized conditions. In mitochondria, energization/de-energization changed the binding capacity for ANS extrapolated for its infinitely high concentration, whereas the apparent Kd value remained unchanged. In submitochondrial particles apparent Kd was changed but the extrapolated maximum binding was not altered. These results are compatible with theoretical considerations assuming a free permeability of mitochondrial membranes to ANS and its distribution according to the transmembrane potential. The spin-labelled cationic amphiphile, 4-(dodecyl dimethyl ammonium)-1-oxyl-2,2,6,6-tetramethyl piperidine bromide (CAT12), was trapped by de-energized mitochondria in such a way that about half of the bound probe became inaccessible to reduction by externally added ascorbate. This inaccessible fraction was increased by energization. This indicates that this cationic probe can penetrate through the inner mitochondrial membrane. De-energization produced a parallel shift of the Lineweaver-Burk plots for the oxidation of external ferrocytochrome c by mitoplasts and of succinate by submitochondrial particles. A similar shift was obtained by a partial inhibition of succinate oxidation by antimycin A. Thus, the observed changes of the kinetics of the two membrane-bound enzyme systems on de-energization can be interpreted as reflecting changes of the control points of mitochondrial respiration rather than changes of the surface potential. It is concluded that neither the fluorescent probe ANS, the spin-labelled amphiphilic cation CAT12, nor the kinetics of some respiratory enzyme systems provide a sufficient proof for changes of the surface potential of the inner mitochondrial membrane upon energization. 相似文献
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Richard Y. Morita 《Origins of life and evolution of the biosphere》1975,6(1-2):37-44
Various processes for the production of carbon dioxide by microorganisms are presented. It is postulated that a microniche developed in a reducing environment; a symbiotic relationship between alga-like organisms and bacterium-like organisms in the microniche governed the production of carbon dioxide resulting in the establishment of the steady state carbon dioxide system in the sea. 相似文献