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101.
Serological studies relating F9 antigen of embryonal carcinoma cells to
at the murineT/t complex have been extended and confirm that only the lethal haplotype t12- and none of the other five lethal haplotypes-affects the quantitative expression of F9 antigen on sperm. Cytotoxicity tests on preimplantation embryos show that t12 homozygotes are less susceptible to antiF9 serum than tw5 homozygotes, and that using specific antimutant haplotype antisera prepared against sperm, t12 antigen is detectable on morulae, whereas tw5 antigen is not. 相似文献
102.
The topographical distribution of genetically defined alloantigens of the bovine erythrocyte was investigated by a serological absorption procedure known as the blocking test. Blocking was observed between the E′1 and Y2 antigens in theB system when these occurred in the same phenogroup. E′1 was also blocked by G and Q′ in the same phenogroup and Y2 was blocked by G. No blocking was observed between specificities residing either in different phenogroups or in different systems. We conclude that the several specificities in a givenB-system phenogroup are carried on a single molecule having multiple antigenic determinants, and that this arrangement is entirely consistent with the hypothesis that these factors are controlled by multiple alleles at a single locus. 相似文献
103.
Contrary to expectations slight undercooking (68.5°C instead of 70°C for 90 min) dramatically increased the shelf-life of chub-packed luncheon meat stored at 25°C. The pH of undercooked chubs fell rapidly to below 5.0 as a result of the growth of enterococci. The accumulated acid prevented the growth of Bacillus spores and gave the luncheon meat a not unpleasant tangy flavour. Degradative changes associated with the spoilage of commercially cooked chub-packed luncheon meat did not occur, even after 42 d storage. Apparently, post-cooking fermentation by enterococci can effectively convert a perishable product into a 'shelf stable' one by lowering the pH below 5.0. 相似文献
104.
M. Moorghen P. Ince Karen J. Finney A. J. Watson A. L. Harris 《In vitro cellular & developmental biology. Animal》1991,27(11):873-877
Summary The in-vitro effects of hydroxyurea 5-FU and 5-FUdR have been extensively studied in experimental systems employing cell-line
techniques. In this study we investigated the effects of these drugs on the levels of incorporation of labeled nucleosides
into DNA in explants of intact rat colonic mucosa maintained in organ culture. The effects of the nucleoside transport inhibitors
nitrobenzylthioinosine (NBMPR) and dipyridamole—which are modulators of antimetabolite cytotoxicity—on the incorporation of
tritiated thymidine [(3H]TdR) into DNA were also studied. The incorporation of tritiated TdR into DNA was reduced by hydroxyurea but was not altered
by either 5-FU or 5-FUdR. The levels of tritiated deoxyuridine were reduced by 5-FU and 5-FUdR in separate experiments; this
is in keeping with thymidylate synthase inhibition. NBMPR and dipyridamole also reduced 3H-TdR incorporation into DNA. These
results can be explained in terms of the known mechanisms of action of these drugs. This experimental model is therefore useful
in assessing the effects of antimetabolites and nucleoside transport inhibitors in intact colonic mucosa. 相似文献
105.
106.
Paula N. Friedman Edith H. Wang Karen Meerovitch Nahum Sonenberg Carol Prives 《Chromosoma》1992,102(1):S60-S66
We have characterized the effects of p53 on several biochemical activities of simian virus 40 (SV40) large tumor (T) antigen. While p53 induced a strong inhibition of the T antigen DNA helicase activity, surprisingly, its RNA helicase activity was stimulated. This supports the liklihood that the DNA and RNA helicase activities of T antigen reflect discrete functions. p53 did not significantly affect the ATP-dependent conversion of T antigen monomers to hexamers. However, the ability of these hexamers to assemble on a DNA fragment containing the viral origin was impaired by p53. Thus, these results suggest that p53 inhibits the function but not the formation of T antigen multimers. This conclusion was further supported by the observation that the addition of a purified p53:T antigen complex was as inhihitory as free p53 to the DNA helicase activity of free T antigen. Thus our data indicates that the targets of p53 inhibition are the functional units of T antigen, namely the hexamers. 相似文献
107.
Effects of chemical composition on nitrogen mineralization from green manures of seven tropical leguminous trees 总被引:8,自引:1,他引:7
Green manures from seven tropical leguminous trees were incubated with soil to determine the rates and controls of net nitrogen release. Fresh green manure (leaves and succulent twigs) was mixed with moist soil and incubated in polyethylene bags. Net N mineralization from green manures was estimated by the accumulation of extractable ammonium and nitrate minus the accumulation in soil alone. Patterns of N mineralization were complex, differed among species, and at 12 weeks ranged from 10 to 65 percent of original green-manure N. Cumulative net N mineralization was negatively correlated with initial soluble polyphenol content in the early phases of decomposition (1 through 8 weeks) and with initial lignin content in later phases (4 through 12 weeks). Neither initial percent N nor lignin: N ratio were strongly correlated with N mineralization. The best chemical index of N release was the initial polyphenol: N ratio. This study confirms previous findings that N mineralization from tropical legumes is controlled more by soluble polyphenols than by lignin or N content. 相似文献
108.
Karen A. Keith Mary C. Duncan Max Murray Ken Bairden Andrew Tait 《International journal for parasitology》1990,20(8):1037-1045
In this study we have shown that NHS-biotin and I125-streptavidin can detect cuticular polypeptides of Ostertagia spp. The labelled polypeptide profile of intact nematodes is simple compared to the profile obtained by labelling homogenates. None of the major internal polypeptides are labelled and the subset of proteins labelled in intact nematodes appears to be mainly surface associated. The results presented here demonstrate that NHS-biotin may be used as a reagent for the analysis of surface polypeptides. The surface polypeptide profiles of the five major developmental stages (L1, L2, L3, L4 and adult) of Ostertagia circumcincta show a series of stage-specific molecules with no polypeptides common to all stages, indicating that the cuticle is a dynamic structure which changes throughout the life cycle. Similarity comparison of Ostertagia ostertagi L3 and L4 stage surface profiles showed that each stage is clearly distinct; comparison of these stages between the two species shows an overall similarity. 相似文献
109.
A ninhydrin-positive, phosphorus-negative lipid from Paracoccus denitrificans ATCC 13543 has been isolated and purified by mild alkaline methanolysis followed by silicic acid column chromatography and preparative thin-layer chromatography. The lipid was identified as an ornithine-containing lipid. The major ester-linked fatty acid was cis vaccenic acid. Major amide-linked fatty acids were 3-OH-20:1 and 3-OH-18:0. Ornithine-containing lipid was a major lipid component of P. denitrificans. Phospholipids made up about 57% and ornithine-containing lipid about 14% of the weight of the total lipid of the organism. The ratios of lipid ornithine: lipid phosphorus were 0.23, 0.65 and 0.58 in cytoplasmic membrane, outer membrane, and an NaCl extract, which is thought to represent chiefly outer membrane, respectively. Thus ornithine-containing lipid appears to be present in larger amounts in outer membrane than cytoplasmic membrane. No substantial variations in lipid ornithine levels were noted in stationary phase versus exposnential phase organisms, organisms grown in complex medium versus organisms grown in minimal medium with and without amino acid supplements, or in organisms grown in low phosphate-containing medium.Non standard abbreviations TLC
thin-layer chromatography
- Tris-HCl
tris(hydroxymethyl)aminomethane hydrochloride
- TMS
trimethylsilyl
- TFA
triluoroacetyl
- NPPN
ninhydrin-positive, phosphorus-negative
- ECL
equivalent chain length 相似文献
110.