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51.
The present paper describes isolation and purification ofa-hemolysin ofEscherichia coli. The optimum production medium was found to be the Todd—Hewitt broth. Out of thirteen fractions obtained after separation
on Sephadex G-200, two fractions possessed the highest relative specific activity. 相似文献
52.
Use of whey for production of exocellular polysaccharide by a mutant strain ofXanthomonas campestris
Growth and kinetics of the production of exocellular polysaccharide was studied in a mutant strain ofXanthomonas campestris lac
+ during cultivation in a submerged culture in a medium containing whey. The maximum production of the polymer was observed
at the initial stage of the stationary growth phase of the culture. The mean production yield was about 1.4%. The results
were comparable with those obtained during cultivation on a lactose medium.
Translated by Č. Novotny 相似文献
53.
Dictyostelium myosin II heavy-chain kinase A (MHCK A) is activated by autophosphorylation. Heparin and DNA, as well as vesicles composed of phosphatidylserine or phosphatidylinositol, were found to increase the initial rate of MHCK A autophosphorylation 5-10-fold in a Ca(2+)-independent manner. The negatively charged molecules also increased the activity of the autophosphorylated MHCK A by about 2-fold. In contrast, positively charged polypeptides such as poly(D-lysine), poly(L-lysine), poly(L-arginine) and histones strongly inhibited (IC50 of 0.5 micrograms/ml) the activity of the active, autophosphorylated MHCK A. Similar levels of inhibition, on a weight basis, were observed for poly(L-lysine) fractions with molecular weights from 3800 to 150,000-300,000. The inhibition was competitive with respect to peptide substrate and mixed with respect to ATP. At much higher concentrations poly(L-lysine) also inhibited the ability of MHCK A to autophosphorylate. It is proposed that negatively charged compounds and autophosphorylation increase the activity of MHCK A by weakening the interaction between the catalytic domain and a positively charged autoinhibitory domain. 相似文献
54.
Summary During subculturing of recombinant Escherichia coli under conditions blocking cloned gene expression the plasmid was structurally stable for 200 generations. However, under conditions permitting foreign gene expression only 10% of plasmid containing cells had this gene functional after 100 generations. 相似文献
55.
Stobadine was found to inhibit the ulcerogenic activity of indomethacin in relation to the dose but was ineffective against the direct necrotizing action of ethanol. It also inhibited gastric acid secretion when administered intraduodenally. Although stobadine is considered to be a scavenger of free radicals, our results indicate that, under the given experimental conditions, it is rather the inhibition of gastric acid secretion that is responsible for its antiulcerogenic effect. The preliminary results do not allow the exclusion of other mechanisms for explaining its antiulcerogenic effect. 相似文献
56.
A method, suitable for the isolation of closed circular plasmid DNA from methylotrophic bacteria is described. Improvement
of cell lysis was achieved by butanol extraction of cells before application of the lytic agent. Using this method, cryptic
plasmids of 7.8, 14, 36 and 200 kb were purified from soil-isolated methylotrophs. 相似文献
57.
A transient 7-fold rise of ppGpp concentration, 2-3-fold increase of pppGpp concentration and 50 % drop of the concentration
of GTP inBacillus megaterium cells immediately after their transfer to the sporulation medium were observed. Actinomycin D, in concentrations inhibiting
RNA synthesis by 95%, blocked the rise of the (p)ppGpp pool and caused an instant several-fold increase of the GTP level.
When the cells were exposed to actinomycin D in the sporulation medium for a 1-h period (time 0–1 h, 1–2 h or 2.20–3.20-h),
they were able to form colonies on nutrient agar after being kept, in addition for 1–2 h in the sporulation medium free of
the antibiotic. The ability of sporulation was, however, markedly limited. The share of cells that could sporulate increased
when the irreversible sporulation phase was reached. 相似文献
58.
J. Matoušek P. Dědič M. J. Beneš P. Kopáček Věra Turková Ludmila Trněná 《Biologia Plantarum》1990,32(6):460-473
A polyspecific antiserum against protein extracted from PSTV-infected tomato leaves was prepared and the IgGs were separated
by affinity chromatography on a beaded cellulose adsorbent with an immobilized “healthy” antigen. The antibody not adsorbed
entered into a preferential reaction with the antigen from PSTV-infected leaves as estimated by an enzyme-linked immunosorbent
assay. The immunochemical reactions did not significantly exceed the control background, if antigens from tomato leaves infected
with potato viruses X, Y and M were analyzed. By immunoblot technique we revealed, however, that several antigens not detected
in healthy leaves appeared in the leaves infected either with PSTV or with viruses X and M. An accumulation of a major antigen
having a molecular mass of about 70 kDa was observed in viroid-infected leaves only, suggesting the specificity for viroid
infection. The antigen was found not to be an alkaline endoproteinase - the pathogenesis-related protein P-69.
Some antigens with molecular masses approximately 38.0, 23.7 and 22 kDa, which occurred in PSTV-infected leaves and in healthy
calluses, were not detectable in PSTV-infected calluses.
No reaction exceeding the control level was observed using enzyme-linked immunosorbent assay for antigens from silver nitrate-treated
tomato leaves, although such leaves showed symptoms similar to that caused by viroids. 相似文献
59.
Deletion of 13q in two patients with retinoblastoma,one probably due to 13q- mosaicism in the mother
Summary We examined the peripheral blood chromosomes of eight patients with retinoblastoma. In two of them an interstitial deletion of 13q was found. The breakpoints were determined as follows: case 1, 13q1221; case 2, 13q1231. In both cases, band 13q14 was deleted. In case 2 the lymphocytes of the mother showed the identical interstitial 13q deletion in 3 of 100 mitoses, thus raising the possibility of maternal origin of the 13q deletion in a child. In one patient, retinoblastoma was unilateral; in the other, bilateral. Both patients were mentally retarded. 相似文献
60.
The induction of gametogenesis in the studied homothallic alga by the transfer to a nitrogen-Less medium leads to an adaptation of the cell population until a dynamic equilibrium is attained. Throughout the adaptation, the homeostatic forces regulating the number of the cells in the population assert themselves on the basis of internal nitrogen circulation. Part of the induced cells which perform no conjugation is probably destroyed by lysing, whereas the cells being just in the pre-Induction phase as well as those having passed the phase without being induced to gametes, continue their cycles by means of the released nitrogenous substances. The conditions which in some cells cause the induction of gametogenesis, produce a partial spontaneous synchronisation in other cells. The course of the cell cycles in parts of the culture may be determined according to the pulses of the increasing number of the zygotes within the whole cell population, if the cell cycles have run at a certain degree of synchrony. The culture conditions which induce gametogenesis cause a quick decrease of the biosyntheses of the RNAs while the biosyntheses of the DNAs are almost maintained at the original level. During the dynamic equilibrium of the population, the average content of the RNAs per cell remains very low, whereas the average content of the DNAs per cell virtually does not change (compared with the original state). 相似文献