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1.
Chemical modification studies on a lectin from Saccharomyces cerevisiae (baker''s yeast). 总被引:3,自引:0,他引:3 下载免费PDF全文
The effect of chemical modification on a galactose-specific lectin isolated from a fatty acid auxotroph of Saccharomyces cerevisiae was investigated in order to identify the type of amino acids involved in its agglutinating activity. Modification of 50 free amino groups with succinic anhydride or citraconic anhydride led to an almost complete loss of activity. This could not be protected by the inhibitory sugar methyl alpha-D-galactopyranoside. Treatment with N-bromosuccinimide and N-acetylimidazole, for the modification of tryptophan and tyrosine residues, did not affect lectin activity. Modification of carboxy groups with glycine ethyl ester greatly affected lectin activity, although sugars afford partial protection. Modification of four thiol groups with N-ethylmaleimide was accompanied by a loss of 85% of the agglutinating activity, and two thiol groups were found to be present at the sugar-binding site of the lectin. Modification of 18 arginine residues with cyclohexane-1,2-dione and 26 histidine residues with ethoxyformic anhydride led to a loss of lectin activity. However, in these cases, modification was not protected by the abovementioned inhibitory sugar, suggesting the absence of these groups at the sugar-binding site. In all the cases, immunodiffusion studies with modified lectin showed no gross structural changes which could disrupt antigenic sites of the lectin. 相似文献
2.
The longitudinal anthropological age changes in a sample of coastal fishermen in West Bengal are discussed. The results show
that some traits follow the trends observed in ageing of Western populations, for instance nasal length and breadth continue
to increase throughout life in both sexes. Stature follows also the trend generally observed: a decrease occurs indeed from
35 years of age in both sexes, the decline is becoming higher with increasing age. The typical ecological conditions of our
population influence the rate of change in other traits, such as weight and biacromial diameter. Weight is known to be influenced
by the nutritional status and the way of life. It explains that in our study of males an early increase of weight and biacromial
diameter is observed first and a decrease afterwards. In females, however, a decrease is observed already from 35 years of
age. This kind of analysis was only possible with the help of longitudinal data and in a well defined population: only longitudinal
data is free from the effect of secular changes and of selective death. 相似文献
3.
Chronic myelogenous leukemia (CML) is a hematologic malignancy characterized by excessive growth of myeloid cells and their progenitors. The proportion of spectrin dimers compared to tetramers extracted from membranes at 4 degrees C, under low ionic strength conditions, increased in CML erythrocytes. These also displayed abnormal thermal sensitivity (between 45 and 46 instead of 49 degrees C). Crosslinking with the bifunctional reagent, dimethyl adipimidate (8.6 A) showed significant organizational modification of not only spectrin, but other cytoskeletal components such as ankyrin, bands 4.2 and 5. Enhanced concanavalin A (Con-A) agglutinability of CML erythrocytes also suggests altered topographic distribution of a functionally important membrane protein, band 3. The anion transport activities of erythrocytes from patients with CML and normal donors were comparable. In CML erythrocytes, significant reduction in the number of ankyrin-binding sites, present in the cytoplasmic domain of band 3, may lead to partial loss of cytoskeletal anchorage to the bilayer and account for their increased Con-A agglutinability and heat sensitivity and may lead to their premature removal from the circulation. 相似文献
4.
Analogues of the des-1-tryptophan,3-beta-cyclohexylalanine-alpha-factor of Saccharomyces cerevisiae, where the glycyl residue of position 9 was replaced by D-Ala, L-Ala, D-Leu, and L-Leu, were synthesized and evaluated by morphogenesis assays and circular dichroism spectroscopy. Synthesis was accomplished in solution phase with mixed anhydrides and p-nitrophenyl active esters as the coupling agents. All crude dodecapeptides were purified to greater than 98% homogeneity by preparative high-performance liquid chromatography on a reversed-phase column. The Gly9, D-Ala9, and D-Leu9 analogues elicited morphogenic alterations in MATa strains of S. cerevisiae at concentrations of 1-2 micrograms/mL and exhibited similar CD patterns in both trifluoroethanol and tris(hydroxymethyl)aminomethane buffer, pH 7.4. In contrast, the L-Ala9 and L-Leu9 analogues were more than 200 times less active in the morphogenesis assay and had markedly different CD spectra. These results demonstrate that the position 9 residue plays an important role in determining the biological activity and solution conformation of alpha-factor. We suggest the presence of a type II beta-turn in the Lys7-Gln10 region when the alpha-factor assumes its biologically active conformation. 相似文献
5.
Proton translocation during the reduction of NO
3
-
, NO
2
-
, N2O and O2, with endogenous substrates, in washed cells of Rhodopseudomonas sphaeroides f. denitrificans was investigated by an oxidant pulse method. On adding NO
2
-
to washed cells, anaerobically in the dark, an alkalinization occurred in the reaction mixture followed by acidification. When NO
3
-
, N2O or O2 was added to cells in the dark or with these compounds and NO
2
-
in light an acidification only was observed. Proton translocation was inhibited by carbonyl cyanide-m-chlorophenyl hydrazone.Valinomycin treated cells produced acid in response to the addition of either NO
3
-
, NO
2
-
, N2O or O2. The proton extrusion stoichiometry (
ratios) in illuminated cells were as follows: NO
3
-
0.5N2, 4.82; NO
2
-
0.5N2, 5.43; N2ON2, 6.20; and O2H2O, 6.43. In the dark the comparable values were 3.99, 4.10, 4.17 and 3.95. Thus, illuminated cells produced higher
values than those in the dark, indicating a close link between photosynthesis and denitrification in the generation of proton gradients across the bacterial cell membranes.When reduced benzyl viologen was the electron donor in the presence of 1 mM N-ethylmaleimide and 0.5 mM 2-n-heptyl-4-hydroxyquinoline-N-oxide in the dark, the addition of either NO
3
-
, NO
2
-
or N2O to washed cells resulted in a rapid alkalinization of the reaction mixture. The stoichiometries for proton consumption,
ratios without a permeant ion were NO
3
-
NO
2
-
,-1.95; NO
2
-
0.5 N2O,-3.03 and N2ON2,-2.02. The data indicate that these reductions occur on the periplasmic side of the cytoplasmic membrane.Abbreviations BVH
reduced benzyl viologen
- CCCP
carbonyl cyanide m-chlorophenyl hydrazone
- DIECA
N, N-diethyl-dithiocarbamate
- HOQNO
2-n-heptyl-4-hydroxyquinoline-N-oxide
- NEM
N-ethylmaleimide 相似文献
6.
Analysis of the signals for polarized transport of influenza virus (A/WSN/33) neuraminidase and human transferrin receptor, type II transmembrane proteins. 总被引:4,自引:2,他引:2 下载免费PDF全文
In polarized MDCK cells influenza virus (A/WSN/33) neuraminidase (NA) and human transferrin receptor (TR), type II glycoproteins, when expressed from cloned cDNAs, were transported and accumulated preferentially on the apical and basolateral surfaces, respectively. We have investigated the signals for polarized sorting by constructing chimeras between NA and TR and by making deletion mutants. NATR delta 90, which contains the cytoplasmic tail and transmembrane domain of NA and the ectodomain of TR, was found to be localized predominantly on the apical membrane, whereas TRNA delta 35, containing the cytoplasmic and transmembrane domains of TR and the ectodomain of NA, was expressed preferentially on the basolateral membrane. TR delta 57, a TR deletion mutant lacking 57 amino acids in the TR cytoplasmic tail, did not exhibit any polarized expression and was present on both apical and basolateral surfaces, whereas a deletion mutant (NA delta 28-35) lacking amino acid residues from 28 to 35 in the transmembrane domain of NA resulted in secretion of the NA ectodomain predominantly from the apical side. These results taken together indicate that the cytoplasmic tail of TR was sufficient for basolateral transport, but influenza virus NA possesses two sorting signals, one in the cytoplasmic or transmembrane domain and the other within the ectodomain, both of which are independently able to transport the protein to the apical plasma membrane. 相似文献
7.
Suman Mishra Nidhi Kundu Ishika Pramanick Anil Kumar Kausik Chattopadhyay Somnath Dutta 《Proteins》2023,91(2):137-146
Thermostable direct hemolysin (TDH) is a ~19 kDa, hemolytic pore-forming toxin from the gram-negative marine bacterium Vibrio parahaemolyticus, one of the causative agents of seafood-borne acute gastroenteritis and septicemia. Previous studies have established that TDH exists as a tetrameric assembly in physiological state; however, there is limited knowledge regarding the molecular arrangement of its disordered N-terminal region (NTR)—the absence of which has been shown to compromise TDH's hemolytic and cytotoxic abilities. In our current study, we have employed single-particle cryo-electron microscopy to resolve the solution-state structures of wild-type TDH and a TDH construct with deletion of the NTR (NTD), in order to investigate structural aspects of NTR on the overall tetrameric architecture. We observed that both TDH and NTD electron density maps, resolved at global resolutions of 4.5 and 4.2 Å, respectively, showed good correlation in their respective oligomeric architecture. Additionally, we were able to locate extra densities near the pore opening of TDH which might correspond to the disordered NTR. Surprisingly, under cryogenic conditions, we were also able to observe novel supramolecular assemblies of TDH tetramers, which we were able to resolve to 4.3 Å. We further investigated the tetrameric and inter-tetrameric interaction interfaces to elaborate upon the key residues involved in both TDH tetramers and TDH super assemblies. Our current structural study will aid in understanding the mechanistic aspects of this pore-forming toxin and the role of its disordered NTR in membrane interaction. 相似文献
8.
Taposhi Hazra Sampa Kundu Subir Bera Tapan Chakraborty Mahasin Ali Khan 《植物分类学报:英文版》2023,61(6):1079-1090
The Ventilago Gaertn. (Rhamnaceae) is widely distributed in pantropical areas of Africa, Asia, and Australia. However, fossil records of this taxon are sparse, which limits understanding of the evolution and biogeographic history of the genus. In the present study, we report and describe two new fossil species of Ventilago, V. siwalika sp. nov. from the Miocene sediments of Himachal Pradesh, western Himalaya, and V. pliocenica sp. nov. from the Pliocene sediments of Jharkhand, eastern India based on single-winged samaras. Ventilago pliocenica is characterized by a prominent midvein, obtuse to sub-round apex with mucronate tip, longitudinal secondary veins extending the full length of the fruit, and reticulate nature of higher-order veins, the presence of equatorial rim, the hypanthium, and short pedicel. On the other hand, V. siwalika is characterized by a prominent midvein, obtuse to sub-round apex with mucronate tip, longitudinal secondary veins extending the full length of the fruit, and reticulate nature of higher-order veins. Our discovery represents the first unambiguous fossil record of single-winged samara of Ventilago from India and provides valuable insights into the evolution of this genus. In this paper, we also review its biogeographic history and add new information to understand its hypothetical migration route. Present and earlier records of Ventilago also suggest that this genus was a common forest element during Neogene (Miocene time) in Asia. 相似文献
9.
Mitochondrial DNA sequence evolution in sharks: rates, patterns, and phylogenetic inferences 总被引:8,自引:0,他引:8
Abundant representation of sharks in the fossil record makes this group a
superb system in which to investigate rates and patterns of molecular
evolution and to explore the strengths and weaknesses of phylogenetic
inferences from molecular data. In this report, the molecular evolution of
the cytochrome b gene in sharks is described and the information related to
results from phylogenetic analysis of the data evaluated in the light of a
phylogeny derived independently of the molecular data. Across divergent
lineages of sharks there is evidence for significant substitution rate
variation, departure from compositional equilibrium, and substantial
homoplasy; nevertheless, the signal of evolutionary history is evident in
patterns of shared transversions and amino acid replacements.
相似文献
10.
There is marked heterogeneity of nucleotide composition in mitochondrial
DNA across divergent animals. Differences in nucleotide composition
presumably reflect differences in directional nucleotide substitution for
A+T or G+C nucleotides. In mitochondrial DNA, there is A+T directional
nucleotide substitution in most (if not all) animals surveyed, and the
magnitude of directional A+T nucleotide substitution differs greatly within
and among groups. Differences in directional nucleotide substitution among
lineages of mammals can be explained by changes in metabolic physiology.
This relationship is thought to be mediated by the effect of oxygen
radicals because these toxic compounds are by-products of aerobic
metabolism and are known mutagens. Association between metabolism and
nucleotide composition provides additional evidence in favor of the
hypothesis that rates and patterns of nucleotide substitution in
mitochondrial DNA can be influenced by factors that impinge on rates of
endogenous DNA damage.
相似文献