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21.
Rogelio O. Arellano Fidel Ramón Amelia Rivera Guido A. Zampighi 《The Journal of membrane biology》1988,101(1):119-131
Summary Lateral axons from the abdominal nerve cord of cray-fish were internally perfused with the calcium receptor calmodulin (CaM) in solutions with low (pCa>7.0) or high (pCa 5.5) calcium concentrations and studied electrophysiologically and morphologically. Results from these experiments show that when the internal solution contains calcium-activated calmodulin (Ca2+-CaM) the junctional resistance between the axons increases from control values of about 60 to 500–600 k in 60 min. In contrast, axons perfused with calmodulin in low calcium solutions maintain their junctional resistance at control levels during the 60-min perfusion. Similar results are obtained when only one or both coupled axons are perfused.The morphological study shows that in the perfused axons the axoplasmic organelles are replaced or grossly perturbed by the perfusion solution up to the region of the synapses. Additionally, in axons perfused with Ca2+-CaM there are regions where the synaptic gap between the membranes decreases from a control 4–6 to 2–3 nm. Both electrophysiological and morphological results can be interpreted as indicating that calcium-activated calmodulin acts directly on the junctional channels to induce their closure. 相似文献
22.
Summary The complete amino acid sequence of the single haemoglobin of the Antarctic fish Aethotaxis mitopteryx DeWitt has been established by automated repetitive Edman degradation on the intact and cleaved (enzymatically and chemically) and chains. A very high sequence identity with other Antarctic fish haemoglobins has been detected. The haemoglobin has a moderate Bohr effect and no Root effect. Organic phosphates and chloride also regulate oxygen binding only to a moderate extent. The lack of Root effect is consistent with the substitution His — Val at the HC3 C-terminal position of the chain. The low overall heat of oxygenation suggests that in this species oxygen transport is an energy-saving process, presumably related to cold adaptation. The comparative analysis of the haemoglobins of Antarctic fishes emphasises some unique features of the oxygen-transport system of A. mitopteryx, which are likely to be related to its also rather unique mode of life.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation 相似文献
23.
Molecular analysis of the avirulence gene avr9 of the fungal tomato pathogen Cladosporium fulvum fully supports the gene-for-gene hypothesis 总被引:12,自引:0,他引:12
Guido F.J.M. Van den Ackerveken Jan A.L. Van Kan Pierre J.G.M. De Wit 《The Plant journal : for cell and molecular biology》1992,2(3):359-366
The interaction between the fungal pathogen Cladosporium fulvum and tomato is supposed to have a gene-for-gene basis. Races of C. fulvum which have 'overcome' the resistance gene Cf9 of tomato, lack the avirulence gene avr9 which encodes a race-specific peptide elicitor. Races avirulent on tomato genotypes carrying the resistance gene Cf9 produce the race-specific peptide elicitor, which induces the hypersensitive response (HR) on those genotypes. The causal relationship between the presence of a functional avr9 gene and avirulence on tomato genotype Cf9 was demonstrated by cloning of the avr9 gene and subsequent transformation of C. fulvum. A race virulent on tomato genotype Cf9 was shown to become avirulent by transformation with the cloned avr9 gene. These results clearly demonstrate that the avr9 gene is responsible for cultivar specificity on tomato genotype Cf9 and fully support the gene-for-gene hypothesis. The avr9 gene is the first fungal avirulence gene to be cloned. 相似文献
24.
25.
One-carbon metabolism in lectin-activated human lymphocytes 总被引:1,自引:0,他引:1
P B Rowe D Sauer D Fahey G Craig E McCairns 《Archives of biochemistry and biophysics》1985,236(1):277-288
Serine is an essential amino acid for the lectin-mediated transformation of human peripheral blood lymphocytes due to the inability of this cell to synthesize sufficient quantities via either the phosphorylated pathway or by reversal of the serine hydroxymethyltransferase reaction to meet the metabolic demands. The level of intracellular serine is tightly regulated, and the culture medium concentration for optimum cellular transformation falls within a relatively narrow range. The three-carbon atom of serine is the major source of one-carbon units required for purine and pyrimidine nucleotide biosynthesis, but the key effect of both serine deprivation and of high medium serine levels would appear to be on protein synthesis. Although an alternative source of one-carbon units, as provided by high levels of formate in the culture medium, can partially reverse the effects of serine deprivation, the only other demonstrable source of one-carbon units, tryptophan, requires serine for its incorporation and subsequent metabolism. Methionine is also essential for lymphocyte transformation and is involved in the synthesis of a small amount of phosphatidylcholine, although most of this phospholipid is provided by choline and lysophosphatidylcholine from the serum-supplemented culture medium. 相似文献
26.
The bacteriophage P22 arc and mnt repressors. Overproduction, purification, and properties 总被引:13,自引:0,他引:13
A K Vershon P Youderian M M Susskind R T Sauer 《The Journal of biological chemistry》1985,260(22):12124-12129
The arc and mnt genes of bacteriophage P22 encode small repressor proteins. We have cloned these genes onto plasmids that overproduce Arc and Mnt to greater than 1% of the soluble cellular protein. Both proteins were purified to greater than 95% homogeneity, and N-terminal sequences and amino acid compositions were determined. These data, in combination with previously determined gene sequences, establish the complete protein sequences for Arc (53 residues) and Mnt (82 residues). Both proteins have melting temperatures between 45 and 55 degrees C and can be renatured to a fully active species. Arc is a dimer in solution and Mnt is a tetramer. 相似文献
27.
Jozef Anné Patrick Verheyen Guido Volckaert Hendrik Eyssen 《Molecular & general genetics : MGG》1985,200(3):506-507
Summary A physical map of the actinophage VWB has been constructed using the restriction endonucleases BglII, ClaI, EcoRI, EcoRV, HindIII, KpnI and SphI. Phage VWB, genome size 47.3 kb, propagates on Streptomyces venezuelae, and it can also lysogenise this species. The three BglII-generated fragments of VWB DNA were cloned in pBR322, and subsequently mapped. In this manner the restriction map of the VWB phage genome was constructed.Abbreviations
dam
DNA adenine methylase activity
- kb
kilobase pairs
- ::
novel joint 相似文献
28.
High-resolution flow cytometry, using avian erythrocytes as an internal standard, was employed to study constitutive genome size variation of G2-phase nuclei of Physarum polycephalum strains during the macroplasmodial stage of their life cycle. Our results document a previously unknown extent of genome size variation and mixoploidy in this organism. The unimodal diploid strain Tu 291 displayed the largest genome of the strains tested; in contrast, the Colonia strain displayed only half of the Tu 291 G2-phase fluorescence, confirming its haploid nature. An additional strain, derived from a recent cross between Lu897 and Lu898 amoebae, must have arisen by selfing (propagation of only one of the parental genomes to the macroplasmodial stage), since its nuclei display close to the haploid G2-phase DNA content. The observation of a small fraction of corresponding diploid nuclei within the haploid population of this strain, while maintained as microplasmodia, supports the notion that meiosis in haploid strains may require the presence of diploid nuclei. Two of the descendants of the prototype haploid Colonia strain, which were kept for extended periods of time in submerse culture, proved to be near diploid and mixoploid. Polyploidization and subsequent loss of DNA thus seems to contribute to the extremes of genome size variation in Physarum. In addition to unimodal fluorescence distributions, a number of diploid strains displayed bi- and even trimodal distributions within harvests of a single G2-phase macroplasmodium. Analysis of these mixoploid strains by means of gaussian curve-fitting suggests that the smaller genome size differences in Physarum may arise in step-wise diminution of DNA in approximate units of 3-5% of the original Tu 291 genome. 相似文献
29.
The rise time, of Signal IIf and the decay time of P-680+ have been measured kinetically as a function of pH by using EPR. The Photosystem II-enriched preparations which were used as samples were derived from spinach chloroplasts, and they evolved oxygen before Tris washing. The onset kinetics of Signal IIf are in agreement, within experimental error, with the fast component of the decay of an EPR signal attributable to P-680+. The signal IIf rise kinetics also show good agreement with published values of the pH dependence of the decay of P-680+ measured optically (Conjeaud, H. and Mathis, P. (1980) Biochim. Biophys. Acta 590, 353–359). These results are consistent with a model where the species Z (or D1) responsible for Signal IIf is the immediate electron donor to P-680+ in tris-washed Photosystem II fragments. 相似文献
30.
Stimulation of Phospholipase A2 and Secretion of Catecholamines from Brain Synaptosomes by Potassium and A23187 总被引:3,自引:3,他引:0
Abstract: Potassium depolarization of rat brain synaptosomes (containing incorporated l-acyl-2-[14C]arachidonyl-phosphatidylcholine) stimulated endogenous phospholipase A1 (EC 3.1.1.32) and A2 (EC 3.1.1.4), as determined by the formation of [14C]lysophosphatidylcholine, [14C]arachidonate, and [14C]prostaglandins, and also stimulated the secretion of [3H]catecholamines. The phospholipase A2 stimulation, dependent on calcium, was elicited in resting synaptosomes by A23187 and was demonstrated with incorporated 1-acyl-2-[l4C]oleoyl-phosphatidylcholine but not with incorporated [I4C]phosphatidylethanolamine or [l4C]phosphatidylserine. Inhibitors of phospholipase A2 [p-bromophenacylbromide (10 μM), trifluoperazine (3 μM), and quinacrine (3 μM) reduced the potassium-stimulated [3H]catecholamine release from synaptosomes to 78, 39. and 55%, respectively, of depolarized controls. The addition of lysophosphatidylcholine increased the release of [3H]norepinephrine to levels observed with potassium depolarization, whereas lysophosphatidylethanolamine, lysophosphatidylserine, and sodium dodecyl sulfate were much less effective. Potassium stimulation of synaptosomes increased the endogenous levels of free arachidonic acid and prostaglandins E2 and F2α. Indomethacin and aspirin decreased the amounts of prostaglandins formed, allowed the accumulation of free arachidonic acid, and diminished the potassium-stimulated release of [3H]dopamine. p-Bromophenacylbromide inhibited the formation of prostaglandin F2α. Addition of prostaglandin E2 inhibited, whereas prostaglandin F2α enhanced the release of [3H]norepinephrine. These results suggest that calcium influx induced by synaptosomal depolarization activates endogenous phospholipase A2, with subsequent formation of lysophosphatidylcholine and prostaglandins, both of which may modulate neurosecretion. 相似文献