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41.
John H. Caldwell Jennifer Van Brunt Franklin M. Harold 《The Journal of membrane biology》1986,89(1):85-97
Summary Injection of depolarizing current into vegetative cells of the water moldBlastocladiella emersonii elicits a regenerative response that has the electrical characteristics of an action potential. Once they have been taken past a threshold of about –40 mV, cells abruptly depolarize to +20 mV or above; after an interval ranging from several hundred milliseconds to a few seconds, the cells spontaneously return to their resting potential near –100 mV. When the action potential was analyzed with voltage-clamp recording, it proved to be biphasic. The initial phase reflects an influx of calcium ions through voltage-sensitive channels that also carry Sr2+ ions. The delayed, and more extended, phase of inward current results from the efflux of chloride and other anions. The anion channels are broadly selective, passing chloride, nitrate, phosphate, acetate, succinate and even PIPES. The anion channels open in response to the entry of calcium ions, but do not recognize Sr2+. Calcium channels, anion channels and calcium-specific receptors that link the two channels appear to form an ensemble whose physiological function is not known. Action potentials rarely occur spontaneously but can be elicited by osmotic downshock, suggesting that the ion channels may be involved in the regulation of turgor. 相似文献
42.
Graham J. Boulnois Jennifer M. Varley Geoffrey S. Sharpe F. Christopher H. Franklin 《Molecular & general genetics : MGG》1985,200(1):65-67
Summary The properties of pLG221, a derivative of the ColIb plasmid carrying the transposon Tn5 are described. This plasmid can be used to introduce Tn5 by conjugation from Escherichia coli into a variety of Gram negative bacteria outside the host range for maintenance of ColIb. Plasmid pLG221, and a similar plasmid pLG223 carrying Tn10 may be of general utility as vectors for transposon-mediated mutagenesis in a variety of Gram negative bacteria. 相似文献
43.
Kwan-Fu Rex Sheu James C. K. Lai Young Tai Kim† Gary Dorante Jennifer Bagg 《Journal of neurochemistry》1985,44(2):593-599
Pyruvate dehydrogenase complex (PDHC) in rat brain was studied immunochemically, using antibodies against the bovine kidney PDHC, by immunoblotting, immunoprecipitation, inhibition of enzyme activity, and enzyme-linked immunoabsorbent assay (ELISA). The immunoblots showed that the antibodies bound strongly to the alpha peptide of the pyruvate dehydrogenase (E1) component, and to the dihydrolipoyl transacetylase (E2) and the dihydrolipoyl dehydrogenase (E3) components of PDHC. A similar immunoblotting pattern was observed in all eight brain regions examined. On immunoblotting of the subcellular fractions, these PDHC peptides were observed in mitochondria and synaptosomes but not in the postmitochondrial supernatants. This agrees with other evidence that brain PDHC is localized in the mitochondria. These results, together with those from sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the immunoprecipitin, also showed that the alpha E1, beta E1, and E3 peptides of rat brain PDHC are very similar in sizes to those of the bovine kidney PDHC, being 42, 36, and 58 kD, respectively. The size of the E2 peptide, 66 kD, is different from that of bovine kidney E2, 73 kD. The relative abundance of PDHC protein in nonsynaptic mitochondria was compared by enzyme activity titration and ELISA. Both methods demonstrated that the amount of PDHC antigen in the mitochondria from cerebral cortex is greater than that in the olfactory bulb mitochondria. This is consistent with the results of the activity measurement. The ELISA also showed that the PDHCs in both mitochondrial populations are antigenically similar.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
44.
The effect of temperature on thermoregulation, metabolism, evaporative water loss and thermal conductance was studied in Gerbillus pusillus . Its resting body temperature (TB) was 34·6°C, approximately 5°C higher than the mean ambient temperature (TA) encountered in its burrow. As TA increased above 34°C, its ability to lose heat to the environment decreased. It overcame this problem by tolerating increases in TB to a non-lethal maximum of 41°C, whilst also eliminating increasing quantities of obligate heat by pulmocutaneous evaporation and conduction.
Metabolic rate was 41% lower than that predicted from Kleiber's (1975) allometric equation. This confers a considerable saving in energy in an environment where food is often scarce, whilst simultaneously reducing heat production and the degree of gaseous exchange in the already oxygen-poor and carbon dioxide-rich environment encountered in the plugged burrows of its natural milieu.
Gerbillus pusillus , therefore, does not maintain strict homeothermy and utilizes a labile TB and reduced metabolic rate as an adaptive mechanism for survival in the arid zones of tropical Africa. 相似文献
Metabolic rate was 41% lower than that predicted from Kleiber's (1975) allometric equation. This confers a considerable saving in energy in an environment where food is often scarce, whilst simultaneously reducing heat production and the degree of gaseous exchange in the already oxygen-poor and carbon dioxide-rich environment encountered in the plugged burrows of its natural milieu.
Gerbillus pusillus , therefore, does not maintain strict homeothermy and utilizes a labile TB and reduced metabolic rate as an adaptive mechanism for survival in the arid zones of tropical Africa. 相似文献
45.
Boggs Christofer H. Rice James A. Kitchell Jennifer A. Kitchell James F. 《Oecologia》1984,62(1):13-17
Summary Predation by naticid gastropods shows evidence of adaptation to maximize the rate of energy intake. The predation rate of Polinices duplicatus feeding on artificially altered, thin-shelled Mercenaria mercenaria was faster than the predation rate on normal Mercenaria. The rate of energy intake was limited by handling time. The time saved by predation on thin-shelled prey was used to forage. Thus time was shown to be valuable to P. duplicatus, and cost-benefit functions using time and energy as currencies are appropriate for estimating dietary efficiency and predicting prey choice.Despite the clear superiority of thin-shelled prey, P. duplicatus did not learn to prefer this novel prey type, suggesting that predator choices are sterotyped, reflecting optima selected over evolutionary time. 相似文献
46.
Organization of the ribosomal ribonucleic acid genes in various wild-type strains and wild-collected strains of Neurospora 总被引:6,自引:0,他引:6
Peter J. Russell Sheryl Wagner Karin D. Rodland Rhonda L. Feinbaum Jennifer P. Russell Marion S. Bret-Harte Stephen J. Free Robert L. Metzenberg 《Molecular & general genetics : MGG》1984,196(2):275-282
Summary The organization of the ribosomal DNA (rDNA) repcat unit in the standard wild-type strain of Neurospora crassa, 74-OR23-1A, and in 30 other wild-type strains and wild-collected strains of N. crassa, N. tetrasperma, N. sitophila, N. intermedia, and N. discreta isolated from nature, was investigated by restriction enzyme digestion of genomic DNA, and probing of the Southern-blotted DNA fragments with specific cloned pieces of the rDNA unit from 74-OR23-1A. The size of the rDNA unit in 74-OR23-1A was shown to be 9.20 kilobase pairs (kb) from blotting data, and the average for all strains was 9.11+0.21 kb; standard error=0.038; coefficient of variation (C.V.)=2.34%. These data indicate that the rDNA repeat unit size has been highly conserved among the Neurospora strains investigated. However, while all strains have a conserved HindIII site near the 5 end of the 25 S rDNA coding sequence, a polymorphism in the number and/or position of HindIII sites in the nontranscribed spacer region was found between strains. The 74-OR23-1A strain has two HindIII sites in the spacer, while others have from 0 to at least 3. This restriction site polymorphism is strain-specific and not species-specific. It was confirmed for some strains by restriction analysis of clones containing most of the rDNA repeat unit. The current restriction map of the 74-OR23-1A rDNA repeat unit is presented. 相似文献
47.
Jennifer Allsop Richard W.E. Watts 《Differentiation; research in biological diversity》1986,32(2):144-147
The overall activity of the purine de novo synthesis pathway and the activities of purine phosphoribosyltransferase in the rat testis were measured at different ages and were correlated with histological observations. Similar studies of the concentration of circulating gonadotrophins and testosterone were performed. The purine phosphoribosyltransferase activities were between two and three orders of magnitude greater than purine de novo synthesis. The peak activity of the purine de novo synthesis pathway coincided with the first appearance of meiosis in the spermatocytes immediately before the luteinising hormone (LH) level rose to its peak. The highest activity of the hypoxanthine phosphoribosyltransferase (HPRT; EC 2.4.2.8) - catalysed purine salvage pathway coincided with the first appearance of mature spermatozoa in the tubules just after the occurrence of peak levels of follicle-stimulating hormone (FSH). These findings are linked to the development of testicular atrophy in cases of severe HPRT deficiency in man. 相似文献
48.
Mavis Hendson Lizzie Askjaer Jennifer A. Thomson Marc van Montagu 《Applied microbiology》1983,45(5):1526-1532
Eighteen strains of Agrobacterium tumefaciens isolated from crown galls were tested for agrocin production. Of six agrocin-producing strains, one (D286) produced a broad-host-range agrocin active against strains carrying nopaline, octopine, and agropine type Ti plasmids. Sensitivity to agrocin D286 was found to map in the 11- to 18-megadalton region of the nopaline Ti plasmid pTiC58. The agrocin was partially purified, and its physical characteristics were consistent with its being a nucleotide, as is agrocin 84. Agrocin D286 was shown to inhibit DNA, RNA, and protein syntheses. Strain D286 spontaneously lost its pathogenicity, and its potential for use in the biological control of crown gall is discussed. 相似文献
49.
1. Mycophenolic acid, an antibiotic of some antiquity that more recently has been found to have marked activity against a range of tumours in mice and rats, strongly inhibits DNA synthesis in the L strain of fibroblasts in vitro. 2. The extent of the inhibition of DNA synthesis is markedly increased by preincubation of the cells with mycophenolic acid before the addition of [(14)C]thymidine. 3. The inhibition of DNA synthesis by mycophenolic acid in L cells in vitro is reversed by guanine in a non-competitive manner, but not by hypoxanthine, xanthine or adenine. 4. The reversal of inhibition by guanine can be suppressed by hypoxanthine, 6-mercaptopurine and adenine. 5. Mycophenolic acid does not inhibit the incorporation of [(14)C]thymidine into DNA in suspensions of Landschütz and Yoshida ascites cells in vitro. 6. Mycophenolic acid inhibits the conversion of [(14)C]hypoxanthine into cold-acid-soluble and -insoluble guanine nucleotides in Landschütz and Yoshida ascites cells and also in L cells in vitro. There is some increase in the radioactivity of the adenine fraction in the presence of the antibiotic. 7. Mycophenolic acid inhibits the conversion of [(14)C]hypoxanthine into xanthine and guanine fractions in a cell-free system from Landschütz cells capable of converting hypoxanthine into IMP, XMP and GMP. 8. Preparations of IMP dehydrogenase from Landschütz ascites cells, calf thymus and LS cells are strongly inhibited by mycophenolic acid. The inhibition showed mixed type kinetics with K(i) values of between 3.03x10(-8) and 4.5x10(-8)m. 9. Evidence was also obtained for a partial, possibly indirect, inhibition by mycophenolic acid of an early stage of biosynthesis of purine nucleotides as indicated by a decrease in the accumulation of formylglycine amide ribonucleotide induced by the antibiotic azaserine in suspensions of Landschütz and Yoshida ascites cells and L cells in vitro. 相似文献
50.
Summary The ultrastructure of the haematopoietic cells in the polychaetes Neoamphitrite figulus Dalyell, Lanice conchilega (Pallas), Arenicola marina (L.), Myxicola infundibulum Renier, Megalomma vesiculusom (Montagu), Sabella penicillus L., are compared: all show similarities in having well developed Golgi, granular endoplasmic reticulum and haemoglobin or chlorocruorin in vesicles, and numerous mitochondria. The porphyrin byproducts of synthesis are combined with iron as haematins within electrondense granules built up from multi-lamellar organelles. The structure of the basal lamina which alone separates the cells from the lumen of the vessels is described and evidence is presented for the method of release of the haem into the plasma by reverse pinocytosis. The cycle of synthesis within the cell is discussed and the process of haem synthesis in annelids is reviewed. The structure of the haemoglobin-containing coelomocytes of Neoamphitrite figulus is briefly described.This work was made possible by an award from the Science Research Council. We would also like to thank the Director and Staff of the Plymouth Laboratory, where some of the work was done, for their hospitality and facilities. 相似文献