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101.
A. Ma Fernández-Peralta J. J. González-Aguilera 《Plant Systematics and Evolution》1986,152(3-4):167-183
Six closely related taxa of the sect.Eusideritis of the genusSideritis (S. leucantha, S. pusilla, S. flavovirens, S. granatensis, S. biflora andS. osteoxylla) are analysed to elucidate their phylogenetic relationships and position within the sect.Eusideritis. Meiotic behaviour, karyotype features, size and fertility of pollen grains, DNA amounts and seed protein profiles are reviewed. A polyploid origin of the group (from x = 7) and the further diversification through dysploidy and chromosome repatterning is postulated.S. osteoxylla is apparently of hybrid origin. 相似文献
102.
A stimulating effect of guanyl nucleotides on the rat-liver soluble cyclic GMP high-affinity phosphodiesterase activity 总被引:1,自引:0,他引:1
The high affinity (low Km) cyclic GMP phosphodiesterase (PDE) is activated by GTP, while the cyclic AMP PDE is not. GTP and its hydrolysis-resistant analogue, guanylylimidodiphosphate (GppNHp), display a half-maximal stimulating effect at almost the same concentration (5 X 10(-6) M). The GTP stimulating effect is not observed when the socalled cyclic GMP low affinity (high Km) PDE is operative. GTP cooperates with the increase of the substrate concentration on removing the IBMX inhibitory effect. The isolation through a classical chromatographic procedure on a DEAE-cellulose column, of a PDE fraction specific for cyclic GMP, results in the loss of the GTP stimulating effect. 相似文献
103.
The isolation of a brain peptide identical to the intestinal peptide PHI (peptide HI) is described. The peptide was isolated from porcine brain extract using a chemical assay method based on its C-terminal isoleucine amide structure. The complete amino acid sequence of the peptide was found to be: His-Ala-Asp-Gly-Val-Phe-Thr-Ser-Asp-Phe-Ser-Arg-Leu-Leu-Gly-Gln-Leu-Ser-Ala- Lys-Lys-Tyr-Leu-Glu-Ser-Leu-Ile-NH2. This sequence is identical to the intestinal peptide thus demonstrating PHI to be a brain-gut peptide. The role of PHI in the central nervous system as a neurotransmitter or neuromodulator is discussed. 相似文献
104.
Inhibition of epidermal metabolism and DNA-binding of benzo[a]pyrene by ellagic acid 总被引:2,自引:0,他引:2
B J Del Tito H Mukhtar D R Bickers 《Biochemical and biophysical research communications》1983,114(1):388-394
Ellagic acid, a common plant phenol, was shown to be a potent inhibitor of epidermal microsomal aryl hydrocarbon hydroxylase (AHH) activity in vitro, and of benzo[a]pyrene (BP)-binding to both calf thymus DNA in vitro and to epidermal DNA in vivo. The in vitro addition of ellagic acid (0.25-2.0 microM) resulted in a dose-dependent inhibition of AHH activity in epidermal microsomes prepared from control or carcinogen-treated animals. The I50 of ellagic acid for epidermal AHH was 1.0 microM making it the most potent inhibitor of epidermal AHH yet identified. In vitro addition of ellagic acid to microsomal suspensions prepared from control or coal tar-treated animals resulted in 90% inhibition of BP-binding to calf thymus DNA. Application of ellagic acid to the skin (0.5-10.0 mumol/10 gm body wt) caused a dose-dependent inhibition of BP-binding to epidermal DNA. Our results suggest that phenolic compounds such as ellagic acid may prove useful in modulating the risk of cutaneous cancer from environmental chemicals. 相似文献
105.
Analysis of the biological effects of specific DNA alkylations by simple alkylating agents is complicated by the variety of sites involved. It is, therefore, of value to be able to incorporate into cellular DNA nucleosides alkylated in a single position, e.g., O6-methyldeoxyguanosine. Such cellular incorporation is particularly difficult to achieve because this nucleoside is rapidly demethylated by adenosine deaminase. We have attempted to achieve such incorporation into the DNA of V79 cells by using coformycin, an inhibitor of adenosine deaminase, and by forcing the cells to depend on exogenous purines by the use of medium containing aminopterin. The DNA of V79 cells exposed to O6-methyl-[8-3H]deoxyguanosine (2.4 μM, sp. act. 14 500 Ci/mole) showed an incorporation level of 4 × 10−8 nucleotides. When 1000-fold higher concentrations were employed (3–15 mM, sp. act. 1.6 Ci/mole), significant cytotoxicity and inhibition of DNA synthesis was observed. However, because it was not economically feasible to administer high specific activity O6-methyldeoxyguanosine to the cells at these concentrations, we could not determine the amount of labeled nucleoside incorporated into DNA. Examination of the frequency of 6-thioguanine-resistant cells in these treated populations showed no significant increase above the background level. Comparison of the cytotoxic effect of O6-methyldeoxyguanosine with deoxyadenosine showed that the toxicity induced by O6-methyldeoxyguanosine could have resulted from mimicry of deoxyadenosine, rather than by incorporation of the alkylated nucleoside itself. 相似文献
106.
In the cucumber ( Cucumis sativus L. cv. Straight Eight) cotyledon expansion assay, cytokinin-stimulated ethylene production was separated from cytokinin-stimulated growth through the use of potassium and calcium salts. Low concentrations of KC1, which dramatically promoted growth induced by cytokinin, inhibited ethylene evolution, while CaCl2 at a concentration that had no effect on growth, strongly promoted the cytokinin-induced ethylene evolution. In contrast to the growth response, stimulation of ethylene production was not directly related to the presence of potassium or calcium but to their relative concentrations. Concentrations of KCl and CaCl2 which promoted ethylene evolution singly, strongly inhibited it when mixed together. Low rates of exogenous ethylene had no effect on the growth response. Both the growth and ethylene responses were found to be general cytokinin phenomena. Cotyledon respiration was promoted by KC1, CaCl2 and cytokinin, but its stimulation was not correlated with either growth or ethylene production. In the presence of KClm cytokinin-induced respiration sharply lowered the content of certain sugars during the large growth response and followed KCl uptake. Analysis of KCl uptake showed that its growth promoting synergism with cytokinin was not due to osmotic effects. 相似文献
107.
Jane E. Langridge-Smith Joseph H. Sellin Michael Field 《The Journal of membrane biology》1983,72(1-2):131-139
Summary In intact ileal mucosa, uptake of SO4 across the brush border membrane requires the presence of Na and is saturable, withK1/2=1.3mm at 140mm Na (P.L. Smith, S.A. Orellana & M. Field, 1981.J. Membrane Biol.
63:199–206). The present study examines the substrate specificities and transport stoichiometry of the Na-dependent SO4 uptake process. The effects of variations in medium anion and cation composition on lumen-to-epithelium influx of SO4 (J
me
SO4
) were determined under short-circuit conditions.J
me
SO4
is inhibited by thiosulfate, but not by phosphate, methylsulfate, vanadate or taurocholate. Cl is weakly inhibitory. Uptake of SO4 is poorly supported by Li, and is unaffected by K, indicating a specific dependence on Na. At low SO4 concentration (0.22mm),J
me
SO4
is a hyperbolic function of medium Na concentration; the corresponding Hill plot is linear with a slope of 1.0, suggesting a transport stoichiometry of 1 Na: 1 SO4. At high SO4 concentration (6.7mm), the Na-dependent SO4 velocity curve is sigmoidal and yields a Hill plot which is again linear but has a slope of 1.56, suggesting transport of more than 1 Na per SO4. SO4 uptake in presence of Na exhibits a dependence on medium pH. At 0.22mm SO4 and 140mm Na,J
me
SO4
was doubled by lowering pH from 7.4 to 6.8. However, at 6.7mm SO4 and 140mm Na, changing pH had no effect onJ
me
SO4
over the range 6.8 to 8.5. The pH dependence ofJ
me
SO4
at 6.7mm SO4 was restored when medium Na was lowered to 3mm, suggesting that pH sensitivity is a function of the concentration of preformed NaSO
4
–
ion pair. The results suggest that SO4 influx across the ileal brush border occurs by electroneutral Na+/NaSO
4
–
or Na+/H+/SO
4
2–
cotransport, the former being favored by high concentrations of Na and SO4. 相似文献
108.
The preparative aspects of isoelectric focusing (IEF) in immobilized pH gradients (IPG) have been investigated as a function of the following parameters: environmental ionic strength (I), gel geometry and shape of pH gradient. As model proteins, hemoglobin (Hb) A and a minor, glycosylated component (HbA1c), with a delta pI = 0.04 pH units, have been selected. The load capacity increases almost linearly, as a function of progressively higher I values, from 0.5 X up to 2 X molarity of buffering Immobiline (pK 7.0) to abruptly reach a plateau at 3 X concentration of buffering ion. The load capacity also increases almost linearly as a function of gel thickness from 1 to 5 mm, without apparently levelling off. When decreasing the pH interval from 1 pH unit (pH 6.8-7.8) to 1/2 pH unit (pH 7.05-7.55) the amount of protein loaded in the HbA zone could be increased by 40%. In 5 mm thick gels, at 2 X pK 7.0 Immobiline concentration, over a 1/2 pH unit span, up to 350 mg HbA (in a 12.5 X 11 cm gel) could be loaded in a single zone, the load limit of the system being around 45 mg protein/ml gel volume. 相似文献
109.
E Gianazza G Dossi F Celentano P G Righetti 《Journal of biochemical and biophysical methods》1983,8(2):109-133
A new technique for generating extended pH gradients (5 pH units) in Immobiline gels is reported. The previously described (J. Biochem. Biophys. Methods 7, 1983, 123-142) five-chamber gradient mixer has been replaced by a two-vessel device. A single mixture of the available Immobilines (pK 3.6, 4.6, 6.2, 7.0, 8.5 and 9.3) is made, with relative concentrations adjusted so as to produce the most uniform buffering power throughout the desired pH interval. This mixture is then divided into two portions, which are titrated to the extremes of the required pH span with an acidic titrant (Immobiline pK approximately 1) and a basic species (Immobiline pK 9.95). Highly reproducible pH gradients (pH 4-9) are thus generated, which appear extremely useful for the first dimensioned of 2-dimensional techniques. Our previously reported computer program has been implemented with an optimization algorithm which, given any cocktail of Immobilines, automatically adjusts the relative initial concentrations until the smoothest possible beta power is found. For the first time it is possible to perform IEF under controlled physico-chemical parameters: pH span and linearity, beta power, ionic strength and molarity of the buffering species. 相似文献
110.
Estimation of pyruvate decarboxylation in perfused rat skeletal muscle 总被引:12,自引:0,他引:12
P Schadewaldt U Münch M Prengel W Staib 《Biochemical and biophysical research communications》1983,116(2):456-461
A total of 46 E. coli strains showing mannose-resistant, P-blood-group independent hemagglutination of human erythrocytes were tested for binding to neuraminic acid. Nine of the strains completely lost their hemagglutination activity after the erythrocytes were treated with neuraminidase. To characterize the receptor structure, different neuraminic acid containing glycoproteins, their desialylated derivatives and neuraminyl oligosaccharides were tested for hemagglutination inhibition. These studies showed that the nine strains had binding specificity for alpha 2-3 linked neuraminic acid. 相似文献