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21.
22.
Derek G. Smyth Frederick C. Battaglia Giacomo Meschia 《The Journal of general physiology》1961,44(5):889-898
A simple method is described for the measurement of pH changes in hemoglobin solutions on oxygenation and reduction. Data are presented establishing the absence of a Bohr effect in p-chloromercuribenzoate [PCMB] treated hemoglobin. The influence of a number of sulfhydryl inhibitors on the Bohr effect of a hemoglobin solution is reported and an interpretation based on steric factors in the protein is proposed. 相似文献
23.
David J. James Andrew J. Passey Derek J. Barbara Michael Bevan 《Plant cell reports》1989,7(8):658-661
The disamed Ti-binary vector pBIN 6 in Agrobacterium tumefaciens has been used in leaf disc transfomations to produce transgenic apple (Malus pumila Mill.) plants with a nomal phenotype except for a somewhat reduced capacity to root. The presence of the genes for nopaline synthase and neomycin phosphotrans ferase (conferring kanamycin resistance), inserted into the host genome by the vector, was confirmed by Southern blot analysis, the detection of nopaline synthase activity and rooting in the presence of the antibiotic.The nopaline synthase gene continued to be expressed in glasshouse-grown plants several months after removal from in vitro growth conditions. 相似文献
24.
Changes in the species composition, photosynthesis, calcification and size-fractionated carbon metabolism by natural phytoplankton assemblages were monitored in three mesocosms under different nutrient conditions during May 1993. In the 3 enclosures, the decline of the diatom-dominated assemblages was followed by the development of a bloom of the coccolithoporid Emiliania huxleyi. Highest growth of E. huxleyi was observed in the mesocosm with a high N : P ratio, suggesting this species is a good competitor at low phosphate concentrations. The transition from diatom- to E. huxleyi-dominated assemblages brought about a sharp reduction of the phytoplankton standing stock and carbon-specific photosynthetic rate. The relative contribution of the smaller size fraction to total photosynthesis increased as the succession progressed. Calcification rate and E. huxleyi cell-specified calcite production were highest during the early stages of development of the E. huxleyi bloom. Distinct changes in the patterns of 14C allocation into biomolecules were noticed during the diatom-E. huxleyi succession. The diatom-dominated assemblage showed high relative 14C incorporation into low molecular weight metabolites (LMWM), whereas proteins and, specially, lipids accounted for the largest proportion of carbon incorporation in the E. huxleyi bloom. The patterns of photoassimilated carbon metabolism proved to be strongly dependent on cellular size, as protein relative synthesis was significantly higher in the smaller than in the larger size fraction, irrespective of the nutrient regime and the successional stage. These results are discussed in relation to the ecological and physiological features of small phytoplankton. 相似文献
25.
We describe the stabilization by pressure of enzymes, including a hydrogenase from Methanococcus jannaschii, an extremely thermophilic deep-sea methanogen. This is the first published report of proteins from thermophiles being stabilized by pressure. Inactivation studies of partially purified hydrogenases from an extreme thermophile (Methanococcus igneus), a moderate thermophile (Methanococcus thermolithotrophicus), and a mesophile (Methanococcus maripaludis), all from shallow marine sites, show that pressure stabilization is not unique to enzymes isolated from high-pressure environments. These studies suggest that pressure stabilization of an enzyme may be related to its thermophilicity. Further experiments comparing the effects of increased pressure on the stability of α-glucosidases from the hyperthermophile Pyrococcus furiosus and Saccharomyces cerevisiae support this possibility. We have also examined pressure effects on several highly homologous glyceraldehyde-3-phosphate dehydrogenases from mesophilic and thermophilic sources and a rubredoxin from P. furiosus. The results suggest that hydrophobic interactions, which have been implicated in the stabilization of many thermophilic proteins, contribute to the pressure stabilization of enzymes from thermophiles. 相似文献
26.
In short-term field trials at combinations of ambient temperature (°C) and insolation (W·m−2), larval Colorado potato beetles (Leptinotarsa decemlineata [Say] [Coleoptera: Chrysomelidae]) were observed after their release on the adaxial surface of leaflets on potato plants
(Solanum tuberosum L. Solanaceae). The larvae either began feeding or moved under the leaflet; mean interval from release to expression of these
behaviors (2.9±0.05 min [n =358]) was independent of air temperature and insolation. Proportion of larvae moving under the
leaflet increased logistically with both air temperature and insolation. A 1 W·m−2 change in insolation (P) evoked the same effect on this proportion as a 0.0838 °C change in air temperature (T
a
), so the two quantities were combined as T*=T
a
+P·0.0838 °C/(W·m−2), which has units of °C. The proportion of larvae moving under the leaflet increased logistically with T*.
In 1-day field trials we monitored air temperature, insolation and proportion of larvae under the leaflet, and compared the
latter to predictions from the logistic regression derived from the short-term trials. Consistently more larvae occurred under
leaflets than predicted from the logistic regression; this bias diminished as T* increased until at T*≥40 °C, observed and predicted proportions were equal. This pattern of deviation from the predictions of the logistic regression
is consistent with a thermoregulatory strategy in which larvae move away from hostile conditions, rather than seek optimal
conditions. 相似文献
27.
Beatriz Ernestina Cabilio Guth Eliana Gonalves Aguiar Patricia Marie Griffin Sonia Regina Testa da Silva Ramos Tnia Aparecida Tardelli Gomes 《Microbiology and immunology》1994,38(9):695-701
Fifty-eight enterotoxigenic Escherichia coli (ETEC) strains, isolated from children with and without diarrhea in Sao Paulo, were examined for the presence of colonization factor antigens (CFAs) and their ability to adhere to HeLa cells. Antisera to CFA/I, the coli surface (CS) antigens CS1CS3, CS2CS3, and CS2 of CFA/II, CFA/III, and CS5CS6 and CS6 of CFA/IV were used. CFAs were identified in 43% of the ETEC strains: 40% of the strains with CFAs harbored CFA/I, 24% carried CFA/II (CS1CS3), 24% carried CFA/IV (CS6), and 12% carried CFA/IV (CS5CS6). CFAs occurred mainly among ETEC strains producing only heat-stable (ST-I) enterotoxin and in strains also producing heat-labile toxin (LT-I). No ETEC strains tested expressed CFA/III. A marked change in serotypes of ST-I-producing strains was found in Sao Paulo between 1979 and 1990. Adherence to HeLa cells was detected in 14% of the ETEC strains. All of them had a diffuse adherence pattern and produced only ST-I, and 88% carried CS6 antigen. 相似文献
28.
Maryna van de Venter Derek Litthauer Willem Oelofsen 《Journal of cellular biochemistry》1994,54(1):1-10
Adipocyte precursors from the stromal vascular fraction of human adipose tissue were allowed to differentiate in serum-free defined medium, whereafter their catecholamine stimulated lipolytic response was compared to that of mature isolated human adipocytes. Seventy-five to ninety percent of the fibroblast-like cells accumulated lipid droplets and glycerol-3-phosphate dehydrogenase activities of 1,000–2,800 mU/mg protein were measured in cell homogenates of differentiated cells. Lipolysis could be stimulated by both isoproterenol and norepinephrine in both differentiated preadipocytes as well as mature adipocytes. The results obtained with β-adrenergic agents suggested the presence of a higher affinity receptor in differentiated preadipocytes as compared to mature adipocytes. Mature adipocytes responded well to β-adrenergic agents, but no antilipolytic α2-adrenergic response was observed in the differentiated preadipocytes. The presence of Gi proteins in the differentiated preadipocytes was suggested by the antilipolytic effect of adenosine as well as the lipolytic activity generated by pertussis toxin. In conclusion, our medium supported the differentiation of a very high percentage of human preadipocytes which developed a sensitive β-adrenergic lipolytic response but which lacked an α2-adrenergic antilipolytic response. 相似文献
29.
In vivo definition of the functional origin of replication (ori(+ )) of the promiscuous plasmid pLS1
The nocR gene of Agrobacterium tumefaciens Ti plasmid pTiT37 is the regulatory gene of the nopaline catabolism (noc) operon of pTiT37. We have cloned and sequenced nocR, which encodes a DNA-binding protein. The deduced amino acid sequence is similar to those of members of the LysR family of prokaryotic activator proteins. Gel retardation experiments demonstrated that the NocR protein binds to the nocR promoter in both the presence and absence of nopaline. The increased mobility of the complex and alterations in the DNase I footprints revealed a nopaline-induced conformational change in the NocR-DNA complex. Sequence analysis of the NocR binding site indicated the presence immediately downstream of the –10 sequence of the nocR promoter of a 12 by putative operator overlapping a consensus gyrase recognition sequence and an 18 by long alternating purine-pyrimidine sequence. These results suggest that nopaline-induced alterations in the NocR protein-nocR promoter complex might control gene expression in the noc operon. 相似文献
30.
Similarly to higher plant root systems, Chlamydomonas reinhardtii Dangeard (UTEX 90) cells exhibited biphasic NO3? uptake kinetics. The uptake pattern was similar in cells cultured in 10 mM NO3? (NO3?-grown), 0.25 mM NO3? (N-limited) or 10 mM NO3? followed by an 18-h period of N-deprivation (N-starved). In all cell types there was an apparent phase transition in uptake at 1.1 mM NO3?, although there were variations in the uptake Vmax of both isotherms. The rate of uptake via isotherm 0 ([NO3?]<1.1 mM) in N-limited cells was higher than that of either NO3?-grown or N-starved cells. In contrast, NO3?-grown and N-limited cells exhibited comparable Vmax values when supplied with 1.1 to 1.8 mM NO3? (isotherm 1). When supplied with 1.6 mM NO3?, both N-limited and N-starved cells exhibited enhanced linear uptake after 60 min of incubation. We ascribed this to an induction phenomenon. This trend was not observed when NO3?-grown cells were supplied with 1.6 mM NO3?, or when N-limited and N-starved cells were supplied with 0.6 mM NO3?. The ‘inducible’ aspect of uptake by N-limited cells was blocked by cycloheximide (10 mg l?1), but not by actinomycin D (5 mg l?1), thus indicating the involvement of a translational or post-translational event. To investigate this phenomenon further, we analysed the cell proteins of N-limited cells supplied with either 0.6 or 1.6 mM NO3? for 90 min, using two-dimensional gel electrophoresis. Comparison of protein profiles enabled the identification of a single cell membrane-associated polypeptide (21 kDa, pI ca 5.5) and ten soluble fraction polypeptides (17–73 kDa, pI ca 5.0 to 7.1) unique to the high NO3? treatment. We propose that the ‘inducible’ portion of NO3? uptake may provide the means by which C. reinhardtii cells regulate uptake in accordance with assimilatory capacity. 相似文献