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Summary The ability of an erpobdellid leech, Erpobdella montezuma, to discriminate between two congeneric amphipod prey (Hyalella montezuma and Hyalella azteca) through mechanoreception was examined. Both E. montezuma and H. montezuma, a pelagic filter feeder, are endemic to the near thermally constant environment of Montezuma Well, Arizona, and form a highly specialized predator-prey relationship. In contrast, H. azteca, a benthic detritivore, is widely distributed throughout North America. Erpobdella montezuma was highly responsive to the prey signals of the endemic H. montezuma and showed only a limited response to H. azteca. An inverse relationship occurred between the frequency of attack and size of the leech. The abilities of Erpobdella punctata and Nephelopsis obscura, neither found in Montezuma Well, to detect the signals of both amphipod prey were also examined. These species with non-specialized diets showed a low response to the signals of both prey species. This study demonstrates that very close predator-prey relationships can develop over evolutionary time in isolated aquatic systems through the use of mechanoreception. 相似文献
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Changes in gene expression during foliar senescence and fruit ripening in tomato (Lycopersicon esculentum Mill.) were examined using in-vitro translation of isolated RNA and hybridization against cDNA clones.During the period of chlorophyll loss in leaves, changes occurred in mRNA in-vitro translation products, with some being reduced in prevalence, whilst others increased. Some of the translation products which changed in abundance had similar molecular weights to those known to increase during tomato fruit ripening. By testing RNA from senescing leaves against a tomato fruit ripening-related cDNA library, seven cDNA clones were identified for mRNAs whose prevalence increased during both ripening and leaf senescence. Using dot hybridization, the pattern of expression of the mRNAs corresponding to the seven clones was examined. Maximal expression of the majority of the mRNAs coincided with the time of greatest ethylene production, in both leaves and fruit. Treatment of mature green leaves or unripe fruit with the ethylene antagonist silver thiosulphate prevented the onset of senescence or ripening, and the expression of five of the seven ripening- and senescence-related genes.The results indicate that senescence and ripening in tomato involve the expression of related genes, and that ethylene may be an important factor in controlling their expression.Abbreviations cDNA
copy-DNA
- MW
molecular weight
- PAGE
polyacrylamide gel electrophoresis
- SDS
sodium dodecyl sulphate 相似文献
35.
Detection of peroxyl and alkoxyl radicals produced by reaction of hydroperoxides with rat liver microsomal fractions. 总被引:2,自引:0,他引:2 下载免费PDF全文
M J Davies 《The Biochemical journal》1989,257(2):603-606
E.s.r. spin trapping using the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was used to detect peroxyl, alkoxyl and carbon-centred radicals produced by reaction of t-butyl hydroperoxide (tBuOOH) with rat liver microsomal fraction. The similarity of the hyperfine coupling constants of the peroxyl and alkoxyl radical adducts to those obtained previously with isolated enzymes suggests that these species are the tBuOO. and tBuO. adducts. The effects of metal-ion chelators, heat denaturation, enzyme inhibitors and reducing equivalents demonstrate that these species arise from reaction of tBuOOH with a haem enzyme such as cytochrome P-450 or cytochrome b5. In the absence of NADPH or NADH the previously undetected peroxyl radical adduct is the major species observed. In the presence of these reducing equivalents the alkoxyl and carbon-centred radical adducts predominate, which is in accord with product studies on similar systems. These results demonstrate that both reductive and oxidative decomposition of tBuOOH can occur in rat liver microsomal fraction with the reductive pathway favoured in the presence of NADH or NADPH. 相似文献
36.
Joint report of the Third International Bovine Lymphocyte Antigen (BoLA) Workshop, Helsinki, Finland, 27 July 1986 总被引:2,自引:0,他引:2
R W Bull H A Lewin M C Wu K Peterbaugh D Antczak D Bernoco S Cwik L Dam C Davies R L Dawkins 《Animal genetics》1989,20(1):109-132
Two hundred and eighty-two alloantisera were submitted by 20 participating laboratories from 13 countries and tested against lymphocytes of 1298 cattle. The cell panel consisted of samples from 38 Bos taurus breeds, 11 Bos taurus crossbreeds, 4 Bos indicus breeds, 6 Bos taurus x Bos indicus, and a variety of other crossbred populations. Using a standardized lymphocytotoxicity test, all 17 previously identified BoLA specificities were confirmed. The workshop produced agreement on 16 new lymphocyte alloantigenic specificities. Three of the new specificities behaved as splits of previously identified BoLA specificities. Four of the new specificities behaved as alleles at the agreed BoLA-A locus. Seven new specificities are tentatively assigned to the BoLA-A locus but require further definition. Two new specificities may represent products of a second closely-linked BoLA locus. 相似文献
37.
Bombesin stimulation of inositol 1,4,5-trisphosphate generation and intracellular calcium release is amplified in a cell line overexpressing the N-ras proto-oncogene. 总被引:4,自引:0,他引:4 下载免费PDF全文
A C Lloyd S A Davies I Crossley M Whitaker M D Houslay A Hall C J Marshall M J Wakelam 《The Biochemical journal》1989,260(3):813-819
Human neutrophils and HL-60 leukaemic cells possess an NADPH oxidase which catalyses superoxide (O2-) formation and is activated by the chemotactic peptide, N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMet-Leu-Phe). In dibutyryl cyclic AMP-differentiated HL-60 cells, ATP and UTP in the presence of cytochalasin B activated O2- formation with EC50 values of 5 microM and efficacies amounting to 30% of that of fMet-Leu-Phe. The potency order of purine nucleotides in activating O2- generation was ATP = adenosine 5'-O-(3-thiotriphosphate) greater than ITP greater than dATP = ADP. Pyrimidine nucleotides activated NADPH oxidase in the potency order UTP greater than dUTP greater than CTP = TTP = UDP. Pertussis toxin completely prevented activation of NADPH oxidase by fMet-Leu-Phe and UTP, whereas the effect of ATP was only partially inhibited. ATP and UTP enhanced O2- generation induced by fMet-Leu-Phe by up to 8-fold, and primed the cells to respond to non-stimulatory concentrations of fMet-Leu-Phe. Activation of NADPH oxidase by UTP but not by ATP was inhibited by various activators of adenylate cyclase. In dimethyl sulphoxide-differentiated HL-60 cells and in human neutrophils, ATP and UTP per se did not activate NADPH oxidase, but they potentiated the effect of fMet-Leu-Phe. Our results suggest that purine and pyrimidine nucleotides act via purino- and novel pyrimidinoceptors respectively, which are coupled to guanine nucleotide-binding proteins leading to the activation of NADPH oxidase. As ATP and UTP are released from cells under physiological and pathological conditions, these nucleotides may play roles as intercellular signal molecules in the activation of O2- formation. 相似文献
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NMR studies of differences in the conformations and dynamics of ligand complexes formed with mutant dihydrofolate reductases 总被引:1,自引:0,他引:1
B Birdsall J Andrews G Ostler S J Tendler J Feeney G C Roberts R W Davies H T Cheung 《Biochemistry》1989,28(3):1353-1362
Two mutants of Lactobacillus casei dihydrofolate reductase, Trp 21----Leu and Asp 26----Glu, have been prepared by using site-directed mutagenesis methods, and their ligand binding and structural properties have been compared with those of the wild-type enzyme. 1H, 13C, and 31P NMR studies have been carried out to characterize the structural changes in the complexes of the mutant and wild-type enzymes. Replacement of the conserved Trp 21 by a Leu residue causes a decrease in activity of the enzyme and reduces the NADPH binding constant by a factor of 400. The binding of substrates and substrate analogues is only slightly affected. 1H NMR studies of the Trp 21----Leu enzyme complexes have confirmed the original resonance assignments for Trp 21. In complexes formed with methotrexate and the mutant enzyme, the results indicate some small changes in conformation occurring as much as 14 A away from the site of substitution. For the enzyme-NADPH complexes, the chemical shifts of nuclei in the bound coenzyme indicate that the nicotinamide ring binds differently in complexes with the mutant and the wild-type enzyme. There are complexes where the wild-type enzyme has been shown to exist in solution as a mixture of conformations, and studies on the corresponding complexes with the Trp 21----Leu mutant indicate that the delicately poised equilibria can be perturbed. For example, in the case of the ternary complex formed between enzyme, trimethoprim, and NADP+, two almost equally populated conformations (forms I and II) are seen with the wild-type enzyme but only form II (the one in which the nicotinamide ring of the coenzyme is extended away from the enzyme structure and into the solvent) is observed for the mutant enzyme complex. It appears that the Trp 21----Leu substitution has a major effect on the binding of the nicotinamide ring of the coenzyme. For the Asp 26----Glu enzyme there is a change in the bound conformation of the substrate folate. Further indications that some conformational adjustments are required to allow the carboxylate of Glu 26 to bind effectively to the N1 proton of inhibitors such as methotrexate and trimethoprim come from the observation of a change in the dynamics of the bound trimethoprim molecule as seen from the increased rate of the flipping of the 13C-labeled benzyl ring and the increased rate of the N1-H bond breaking. 相似文献
40.
The potential role of human kidney cortex cysteine proteinases in glomerular basement membrane degradation 总被引:3,自引:0,他引:3
(1) The degradation of glomerular basement membrane and some of its constituent macromolecules by human kidney lysosomal cysteine proteinases has been investigated. Three cysteine proteinases were extracted from human renal cortex and purified to apparent homogeneity. These proteinases were identified as cathepsins B, H and L principally by their specific activities towards Z-Arg-Arg-NHMec, Leu-NNap and Z-Phe-Arg-NHMec, respectively, and their Mr on SDS-polyacrylamide gel electrophoresis under reducing conditions. (2) Cathepsins B and L, at acid pH, readily hydrolysed azocasein and degraded both soluble and basement membrane type IV and V collagen, laminin and proteoglycans. Their action on the collagens was temperature-dependent, suggesting that they are only active towards denatured collagen. Cathepsin L was more active in degrading basement membrane collagens than was cathepsin B but qualitatively the action of both proteinases were similar, i.e., at below 32 degrees C the release of an Mr 400,000 hydroxyproline product which at 37 degrees C was readily hydrolysed to small peptides. (3) In contrast, cathepsin H had no action on soluble or insoluble collagens or laminin but did, however, hydrolyse the protein core of 35S-labelled glomerular heparan sulphate-rich proteoglycan. (4) Thus renal cysteine proteinases form a family of enzymes which together are capable of degrading the major macromolecules of the glomerular extracellular matrix. 相似文献