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21.
Temperature-sensitive (ts) mutants of the cyanobacteriumAnabaena variabilis ATCC 29413 were isolated following mutagenesis with N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) and post-treatment with metronidazole
at 40°C. Of the 8000 clones isolated and tested, six mutants were conditionally lethal at the restrictive temperature (40°C).
All the ts mutants exhibited differences in their rates of growth, chlorophyll content, pigment (phycocyanin and/or chlorophyll)
ratios, heterocyst frequency, oxygen evolution and nitrogenase activity at the permissive temperature (28°C). A gradual loss
of all the above features occurred after a period of 3 d at 40°C, followed by lysis of the cultures. Cessation of nitrogenase
activity was found to be different in the different ts mutants. The temperature-sensitive nature of the mutants is suggested
to be due to an impairment in iron metabolism since addition of ferric citrate to cultures at 40°C restored the ability to
grow, produce heterocysts and fix nitrogen. 相似文献
22.
Anabaena torulosa exhibited fructose-dependent growth, heterocyst differentiation and N2 fixation in nitrate-free (diazotrophic) cultures in photoheterotrophic and chemoheterotrophic conditions. The incorporation
of nitrate into such cultures inhibited the formation of heterocysts and N2 fixation. The rate of NO
3
−
uptake byA. torulosa in photoautotrophic, photoheterotrophic and chemoheterotrophic conditions was similar but it increased by 100% in phototrophic
conditions. The activity of glucose-6-phosphate dehydrogenase was found to be maximum in phototrophic and photoheterotrophic
conditions. Ferredoxin-NADP+ reductase, nitrate reductase and glutamate-ammonia ligase activities suggest that nitrate utilization takes place in nonphotosynthetic
conditions. 相似文献
23.
Blood serum total cholesterol levels of crossbred Taur-indicus donor cows (n=22), in their 1st to 4th parity, were studied as an indicator of embryo yield. These cows were superovulated either with FSH or PMSG + anti-PMSG on the 12th day of the synchronized estrous cycle. The total and transferable number of embryos did not differ significantly between the treatment groups. The number of corpora lutea and total and transferable embryos in donors having total cholesterol levels <140 mg/dl were significantly (P < 0.05) lower than those of cows having >140 mg/dl, indicating that low total cholesterol levels might adversely affect superovulatory response. Thus, estimation of total cholesterol concentrations of potential donors can be a useful tool for predicting superovulatory responses. 相似文献
24.
J. Morales-Ventura S. Nandini S. S. S. Sarma 《Zeitschrift fur angewandte Ichthyologie》2004,20(5):417-421
Survival during early fish larval stages depends largely upon the availability of appropriate prey. Studied were the functional responses from hatching to 6 weeks of age of whitefish (Charal) (Chirostoma riojai) larvae that were offered selected rotifers (Brachionus rotundiformis and B. rubens) and cladocerans (Moina macrocopa and Ceriodaphnia dubia). The experiments were conducted in a 50 ml medium at a salinity of 2 g L?1. Each treatment used four replicates. Rotifers were introduced at densities of 0.5, 1, 2, 4, 8 and 16 individuals ml?1 and cladocerans at 0.1, 0.2, 0.4, 0.8, 1.6, 3.2, 4.8 and 6.4 individuals ml?1. Two larvae, previously starved for 2 h, were introduced into each test jar and allowed to feed for 45 min. The difference between the initial and final zooplankton density represented prey consumption. C. riojai larvae showed Type II functional response curves, i.e. they consumed more zooplankton with increasing prey availability; above a certain prey density (8–16 individuals ml?1 in rotifers and 3.2–6.4 individuals ml?1 in cladocerans) the consumption rate tended to stabilize in most trials. Results are discussed in relation to aquaculture. 相似文献
25.
Laboratory-cultured Streptocephalus torvicornis were offered 8 concentrations (from 6 to 800 ind. ml–1) of Anuraeopsis fissa for periods of 2 h 30 min. Two size classes, small (male: 14.7 mm± 1.6, female: 15.4 mm± 1.3) and large (male: 20.0 mm±2.0, female: 23.1 mm± 1.5), of S. torvicornis were used. Functional response for large S. torvicornis (both sexes) plateaued at 400 rotifers ml–1, while in small specimens it did so at 200 prey ml–1. Females consumed significantly more (30%) prey than males. Large males consumed maximum 4730 rotifers h–1, females 6560 h–1. 相似文献
26.
G M Ledda A Columbano P M Rao S Rajalakshmi D S Sarma 《Biochemical and biophysical research communications》1980,95(2):816-821
In order to characterize rat liver DNA replicated on a carcinogen-damaged template, the replicated DNA was treated with S1-nuclease and the release of (14C)-dimethyl-nitrosamine induced 06-methylguanine, a lesion associated with miscoding and N-7-methylguanine, a lesion that does not miscode were monitored. The results indicated that both the methylated guanines became susceptible to S1-nuclease upon replication. However, a greater percentage of 06-methylguanine (22% of the total 06-methylguanine present in the DNA) compared to N-7-methylguanine (4% of the total N-7-methylguanine present in the DNA) was rendered acid soluble by S1-nuclease. The preferential release of 06-methylguanine compared to N-7-methylguanine from replicated DNA was interpreted to indicate its occurrence in local denatured regions probably generated as a result of misbase pairing. 相似文献
27.
Crystals of lysozyme from Streptomyces erythraeus are orthorhombic, space group P212121 with unit cell dimensions: and ; and one molecule, of molecular weight about 18,500, per asymmetric unit. 相似文献
28.
In order to obtain information about the conformational characteristics at the nearestneighbor level in the 2′-O-methylated region of t-RNA, as well as in the bizarre 5′-terminus of eucaryotic mRNA, a detailed nuclear magnetic resonance study of 2′-O-methyl-cytidylyl-(3′ → 5′)-cytidine (CmpC) was conducted. Proton spectra were recorded at 270 MHz in the Fourier mode in D2O solutions, 0.01M, pD 7.3 in the temperature range 5–80°C. Complete accurate sets of nmr parameters were derived for each of the nucleotidyl units by a combination of homo-nuclear decouplings and simulation iteration methods. The data were translated into conformational parameters using procedures developed in earlier studies from these laboratories. It is shown that the ribofuranose ring exists at a 2E ? 3E equilibrium with clear preference [(75–80)%] for the 3E mode. The C(4′)-C(5′) and C(5′)-O(5′) bonds form a stable conformational network with outspoken preference for conformers in which Ψ1, Ψ2 ? 60° and ?2 ? 180°. The orientation of the 3′-phosphate and 2′-O-methyl groups is such that ?1′ ? 210° and ?″ ? 60°. The phosphodiester bonds are flexible and shift trends for base, H(1′), and H(5″) suggest the existence of a conformational blend of right-handed stack (g?g?), left-handed stack (g+g+), and unstacked arrays (tg? and tg+). Elevation of temperature perturbs the 2E ? 3E equilibrium accompanied with modest depopulation of ψ1, ψ2 ? 60° and ?2 ? 180° conformers. The major effect of elevation of temperature is in the increase of unstacked arrays at the expense of g?g? and g+g+ conformers. The shift trend of Cmp-H(3′) with temperature shows that torsional variation about O(3′)-P is facilitated by increase in temperature and the preferred rotamer about O(3′)-P in the unstacked form is t (ω1′ = 180°). A detailed comparison of the aqueous solution conformations of CpC and CmpC reveals that 2′-O-methylation causes: (i) a reduction in the magnitude of χ1; (ii) an increase in the population of 3E pucker at the 3′-nucleotidyl unit; and (iii) modest perturbations in the O(3′)-P and P-O(5′) bond conformations. Comparison of the aqueous solution conformations of AmpA and CmpC makes clear that the conformational properties of pyrimidine-pyrimidine and purine-purine dimers which carry a 2′-O-methylated 3′-nucleotidyl unit are significantly different. 相似文献
29.
The multiplication of A. culbertsoni in the peptone medium was not inhibited by 10-20 mM concentration of alpha-difluoromethyl ornithine (DMFO) while a partial and transient inhibition of cell multiplication was observed by 10-20 mM DFMO in proteose peptone, yeast extract, glucose (PYG) medium. Ornithine decarboxylase (ODC) activity in the cells and cell free extracts was strongly inhibited by DFMO, excluding enzyme refractoriness and impermeability of cells for DFMO as the possible causes of DFMO resistance. The presence of polyamines in the peptone and PYG media as well as uptake of polyamines by the amoebae has been demonstrated. The growth and multiplication of A. culbertsoni in chemically defined medium was not affected by 1-5 mM DFMO while 10-20 mM DMFO yielded partial inhibition. A lowering of diaminopropane levels and enhancement of spermidine levels was observed in DFMO inhibited cells and level of ODC was drastically reduced in the inhibited cultures. Uptake of polyamines from the growth media may partly account for DFMO resistance of A. culbertsoni. Alternative mechanisms for DFMO resistance are indicated. 相似文献
30.
A Srinivasan E P Reddy P S Sarma R A Schulz 《Biochemical and biophysical research communications》1979,91(1):239-246
Caffeine was found to inhibit RNA-dependent DNA polymerase activity of Rauscher leukemia virus when endogenous viral RNA and poly(rA)·(dT)12–18 were used as templates. Similar results were also obtained with purified RNA-dependent DNA polymerase (deoxynucleoside triphosphate; DNA nucleotidyl transferase; EC 2.7.7.7) from avian myeloblastosis virus (AMV) utilizing 70S and 35S RNA of AMV, poly(rA)·(dT)12–18, globin mRNA and activated calf thymus DNA as templates. The “caffeine effect” was evident only when it was present during the initiation of polymerization reaction. Increasing the template concentration in the reaction mixture partly reversed the effect of caffeine. Of the analogs of caffeine tested, only theophylline inhibited AMV DNA polymerase, whereas aminophylline showed no effect. 相似文献