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221.
The influence of moulded hay (Alternaria alternata, Epicoccum nigrum, Mucor racemosus, Ulocladium chartarum) and the efficiency of Vitamin B1 substitution to cope these effects on rumen protozoa was investigated using the longterm rumen simulation technique (RUSITEC) for about 25 days. Moulded hay affected medium-sized protozoa to a different extent (Alternaria alternata: ?16 %, Epicoccum nigrum: ?27 %, Mucor racemosus: ?9 %, Ulocladium chartarum: +2 %). The vitamin B1 substitution had positive effects during the feeding of Mucor racemosus and Ulocladium chartarum. 相似文献
222.
Jerzy Chelkowski Piotr Zajkowski Marcin Zawadzki Juliusz Perkowski 《Mycotoxin Research》1987,3(1):25-32
An isolated rat liver was perfused with deoxynivalenol (DON) at a dose of 3 mg in a recirculating perfusion system. To identify glucuronide conjugates equal amounts of bile samples, perfusate and liver homogenates were incubated with and without (control) a β-glucuronidase preparation and analyzed by thin layer chromatography and capillary gas liquid chromatography — chemical ionization mass spectrometry. A total of 40.4% of the administered dose of DON was found to be conjugated with glucuronic acid (perfusate 20.4%, bile 19.2%, liver 0.8%), while only 1.3% of the parent DON (perfusate 1.1%, bile 0.2%) was detected. The cleavage of DON-glucuronide was demonstrated by incubating DON-glucuronide containing bile samples with intestine contents under anaerobic conditions. 相似文献
223.
Development of High-Frequency Delivery System for Transposon Tn919 in Lactic Streptococci: Random Insertion in Streptococcus lactis subsp. diacetylactis 18-16 总被引:6,自引:3,他引:3
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The conjugative transposon Tn919, originally isolated in Streptococcus sanguis FC1, is capable of low-frequency transfer (10−7 and 10−8 per recipient) on membrane filters to a wide number of streptococcal recipients including the industrially important lactic streptococci. The introduction of pMG600 (Lac+ Lax−; a lactose plasmid capable of conjugative transfer at high frequencies and which, in certain hosts, confers an unusual clumping phenotype) into a Streptococcus lactis CH919 donor, generating S. lactis CH001, resulted in a significant improvement in the transfer frequency of Tn919 to S. lactis CK50 (1.25 × 10−4 per recipient). In addition, these matings could be performed on agar surfaces, allowing the recovery of a greater number of recipients than with filter matings. Tn919 also transferred at high frequency to S. lactis subsp. diacetylactis 18-16S but not to Streptococcus cremoris strains. Insertion in 18-16S transconjugants generated from filter matings with an S. lactis CH919 donor was random, occurring at different sites on the chromosome and also in plasmid DNA. Thus, the conditions necessary for the practical exploitation of Tn919 in the targeting and cloning of genes from a member of the lactic streptococci, namely, high-frequency delivery and random insertion in host DNA, were achieved. 相似文献
224.
Summary Standard laboratory yeast strains have from four to five genes encoding the methionine initiator tRNA (IMT). Strain S288C has four IMT genes with identical coding sequences that are colinear with the RNA sequence of tRNA
I
Met
. Each of the four IMT genes from strain S288C is located on a different chromosome. A fifth IMT gene with the same coding sequence is present in strain A364A but not in S288C. By making combinations of null alleles in strain S288C, we show that each of the four IMT genes is functional and that tRNA
I
Met
is not limiting in yeast strains with three or more intact genes. Strains containing a single IMT2, 3 or 4 gene grow only after amplification of the remaining IMT gene. Strains with only the IMT1 gene intact are viable but grow extremely slowly; normal growth is restored by the addition of another IMT gene by transformation, providing a direct test for IMT function.Abbreviations
IMT and imt
(imt=initiator methionine tRNA), designate the genotype of the wild-type and the mutant alleles respectively, of the initiator methionine transfer RNA gene
- met-tRNA
I
Met
methionylated initiator methionine transfer RNA
- eIF-2
eukaryotic initiation factor two
- GTP
guanosine 5-triphosphate
The calculation of Td values (the temperature at which half of the duplex is dissociated) for oligonucleotides used as probes in hybridizations was based on the assumption that the increase in Td value was 4° C for each G:C base pair and 2° C for each A:T base pair (Wallace et al. 1981) 相似文献
225.
The kinetic properties of ribulose 1,5-bisphosphate carboxylase(RuBPC) appear to have been modified during evolution of photosynthesisto adjust to changes in substrate availability. C4 plants areconsidered to have a higher concentration of CO2 available toRuBPC than C3plants. In this study, the Km(CO2 and catalyticcapacity (kcat) of RuBPC and the ratio of RuBPC protein to totalsoluble protein from several Flaveria species, including C3,C3-C4 intermediate, and C4 species, were determined. The C3and intermediate species had similar Km(CO2) values while theC4 species on average had higher Km(CO2) values. The mean ratioof Kcat/Km for species of each group was similar, supportingthe hypothesis that changes in Km and Kcat, are linked. Theallocation of total soluble protein to RuBPC was lowest in theC4 Flaveria species, intermediate in the C3-C4 species, andhighest in the C3 species. The results suggest that during evolutionof C4 photosynthesis adjustments may occur in the quantity ofRuBPC prior to changes in its kinetic properties. (Received January 4, 1989; Accepted April 11, 1989) 相似文献
226.
Rates of mutation to growth factor autonomy and tumorigenicity differ in hematopoietic stem and precursor cells expressing the multilineage colony-stimulating factor gene. 总被引:2,自引:0,他引:2
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C Laker N Kluge C Stocking U Just M J Franz W Ostertag J F DeLamarter M Dexter E Spooncer 《Molecular and cellular biology》1989,9(12):5746-5749
At least two separate but interdependent events are required to attain autonomous growth as a consequence of ectopic expression of the multilineage colony-stimulating factor gene in hematopoietic progenitor cells. The rate at which the second event occurs is more than 3 orders of magnitude higher in precursor cell lines (FDC-P1 or FDC-P2) than in stem cell lines (FDC-Pmix). Autonomous, but not density-dependent, growth is tightly coupled to tumorigenicity in precursor cells; however, neither growth-factor-independent nor autonomously growing stem cell lines are tumorigenic. 相似文献
227.
228.
229.
Curtis W. Hoganson Demetrios F. Ghanotakis Gerald T. Babcock Charles F. Yocum 《Photosynthesis research》1989,22(3):285-293
Manganese in the oxygen-evolving complex is a physiological electron donor to Photosystem II. PS II depleted of manganese may oxidize exogenous reductants including benzidine and Mn2+. Using flash photolysis with electron spin resonance detection, we examined the room-temperature reaction kinetics of these reductants with Yz
+, the tyrosine radical formed in PS II membranes under illumination. Kinetics were measured with membranes that did or did not contain the 33 kDa extrinsic polypeptide of PS II, whose presence had no effect on the reaction kinetics with either reductant. The rate of Yz
+ reduction by benzidine was a linear function of benzidine concentration. The rate of Yz
+ reduction by Mn2+ at pH 6 increased linearly at low Mn2+ concentrations and reached a maximum at the Mn2+ concentrations equal to several times the reaction center concentration. The rate was inhibited by K+, Ca2+ and Mg2+. These data are described by a model in which negative charge on the membrane causes a local increase in the cation concentration. The rate of Yz
+ reduction at pH 7.5 was biphasic with a fast 400 s phase that suggests binding of Mn2+ near Yz
+ at a site that may be one of the native manganese binding sites.Abbreviations PS II
Photosystem II
- YD
tyrosine residue in Photosystem II that gives rise to the stable Signal II EPR spectrum
- Yz
tyrosine residue in Photosystem II that mediates electron transfer between the reaction center chlorophyll and the site of water oxidation
- ESR
electron spin resonance
- DPC
diphenylcarbazide
- DCIP
dichlorophenolindophenol 相似文献
230.
Lars-Gunnar Franzén Gerhard Frank Herbert Zuber Jean-David Rochaix 《Plant molecular biology》1989,12(4):463-474
cDNA clones encoding two Photosystem I subunits of Chlamydomonas reinhardtii with apparent molecular masses of 18 and 11 kDa (thylakoid polypeptides 21 and 30; P21 and P30 respectively) were isolated using oligonucleotides, the sequences of which were deduced from the N-terminal amino acid sequences of the proteins. The cDNAs were sequenced and used to probe Southern and Northern blots. The Southern blot analysis indicates that both proteins are encoded by single-copy genes. The mRNA sizes of the two components are 1400 and 740 nucleotides, respectively. Comparison between the open reading frames of the cDNAs and the N-terminal amino acid sequences of the proteins indicates that the molecular masses of the mature proteins are 17.9 (P21) and 8.1 kDa (P30). Analysis of the deduced protein sequences predicts that both subunits are extrinsic membrane proteins with net positive charges. The amino acid sequences of the transit peptides suggest that P21 and P30 are routed towards the lumenal and stromal sides of the thylakoid membranes, respectively.Abbreviations OEE1, 2 and 3
oxygen evolution enhancer proteins 1, 2 and 3
- Rubisco
ribulose bisphosphate carboxylase/oxygenase
- PS
photosystem
- P21 and P30
C. reinhardtii thylakoid polypeptides 21 and 30 相似文献