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991.
A cell-free extract, prepared from Aspergillus parasiticus ATCC 15517 grown in synthetic medium, was active in converting [14C]sterigmatocystin into aflatoxin B1 in the presence of reduced nicotinamide adenine dinucleotide phosphate. The activity was demonstrated by the time course of conversion and the linear dependence of the yield of product on enzyme concentrations. Optimum activity was obtained at pH 7.5 to 7.8 at 27 C. The results confirm sterigmatocystin as a biogenetic precursor of aflatoxin B1. Techniques were developed for enzymatic studies on aflatoxin biosynthesis. 相似文献
992.
The rudimentary wing phenotype was examined in detail, using six different alleles of rudimentary, and a number of points about the genesis of the r phenotype were made. (1) All of the r alleles in which the wings are defective produce wings in which the area of individual hair cells is reduced. The more severely affected the allele, the greater is the reduction in wing cell area. This reduction in area is probably uniform throughout the wing rather than localized to specific wing regions. (2) The total number of cells per wing is also greatly reduced in phenotypically r wings. As with cell area, the more severely affected the allele, the greater the reduction in cell number. However, the reduction in cell number is not uniform throughout the wing. In the less severely affected alleles, the cell number reduction is much greater in those regions of the wing which are drastically altered in shape (truncated), while those wing regions which show only slight size reductions but no overall shape changes have near normal numbers of cells. In the most deformed wings, there is a reduction in cell number throughout the wing, but again those regions with are severely truncated are the most drastically reduced in cell number. Measurements of the amount of chitin per wing indicated that the three most severely affected alleles had as much or more chitin than the wild type. It is suggested that overproduction of chitin in these alleles prevents normal expansion of the wing cells, thus increasing the severity of the wing defect. Finally, the validity and limitations of a quantitative measure of the r phenotype were defined. This measure was utilized to demonstrate a clear-cut effect of nutrition on the expression of the r phenotype. 相似文献
993.
994.
The excretion of mutagens in the urine of cigarette smokers was studied as a model for absorption and elimination of complex carcinogenic and mutagenic mixtures in humans. Urine was collected from an occasional smoker who smoked 1 cigarette (17 mg tar/cigarette) and from a heavy smoker (smokes approximately 20 cigarettes/day) who quit for 2 days and then resumed smoking. Urine samples were collected for 6 days, including a 2-day pre-smoking period for the occasional smoker and pre-abstention period for the heavy smoker, respectively. Mutagen excretion patterns were determined by extracting the mutagens in each urine sample with XAD-2 resin and testing the extract in a microsuspension modification of the Salmonella/microsome liquid-incubation assay using bacterial strain TA98 with metabolic activation. Peak mutagenic activity of the urine collected from the two smokers appeared 4-5 h after the beginning of smoking. Activity decreased to pre-smoking "baseline' levels in approximately 12 h for the occasional smoker, and the activity for the heavy smoker approached the occasional smoker's 'baseline' in approximately 18 h after the cessation of smoking. The mutagen excretion patterns of the occasional smoker after smoking a single cigarette suggests that, the mutagens, as detected by the Salmonella assay, are absorbed rapidly (3-5 h) and are eliminated from the body following first order kinetics. The excretion rate constant for the occasional smoker was approximately 0.1 h-1 and the half-life (T1/2) was approximately 7 h. 相似文献
995.
Drosophila topoisomerase II double-strand DNA cleavage: analysis of DNA sequence homology at the cleavage site. 总被引:44,自引:16,他引:28
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In order to study the sequence specificity of double-strand DNA cleavage by Drosophila topoisomerase II, we have mapped and sequenced 16 strong and 47 weak cleavage sites in the recombinant plasmid p pi 25.1. Analysis of the nucleotide and dinucleotide frequencies in the region near the site of phosphodiester bond breakage revealed a nonrandom distribution. The nucleotide frequencies observed would occur by chance with a probability less than 0.05. The consensus sequence we derived is 5'GT.A/TAY decrease ATT.AT..G 3', where a dot means no preferred nucleotide, Y is for pyrimidine, and the arrow shows the point of bond cleavage. On average, strong sites match the consensus better than weak sites. 相似文献
996.
Byrnes W. C.; Clarkson P. M.; White J. S.; Hsieh S. S.; Frykman P. N.; Maughan R. J. 《Journal of applied physiology》1985,59(3):710-715
Perceived muscle soreness ratings, serum creatine kinase (CK) activity, and myoglobin levels were assessed in three groups of subjects following two 30-min exercise bouts of downhill running (-10 degrees slope). The two bouts were separated by 3, 6, and 9 wk for groups 1, 2, and 3, respectively. Criterion measures were obtained pre- and 6, 18, and 42 h postexercise. On bout 1 the three groups reported maximal soreness at 42 h postexercise. Also, relative increases in CK for groups 1, 2, and 3 were 340, 272, and 286%, respectively. Corresponding values for myoglobin were 432, 749, and 407%. When the same exercise was repeated, significantly less soreness was reported and smaller increases in CK and myoglobin were found for groups 1 and 2. For example, the percent CK increases on bout 2 for groups 1 and 2 were 63 and 62, respectively. Group 3 demonstrated no significant difference in soreness ratings, CK activities, or myoglobin levels between bouts 1 and 2. It was concluded that performance of a single exercise bout had a prophylactic effect on the generation of muscle soreness and serum protein responses that lasts up to 6 wk. 相似文献
997.
Two mutant strains of Aspergillus parasiticus, both deficient in aflatoxin production, were used to elucidate the biosynthetic pathway of this mycotoxin. One of the mutants, A. parasiticus ATCC 24551, was capable of accumulating large amounts of averufin, and the other, A. parasiticus 1-11-105 wh-1, accumulated versicolorin A. The averufin producing mutant efficiently converted 14C-labeled versiconal acetate, versicolorin A, and sterigmatocystin into aflatoxin B1 and G1, indicating that averufin preceded these compounds in the aflatoxin biosynthetic pathway. In the presence of dichlorvos (dimethyl 2,2-dichlorovinyl phosphate), a known inhibitor of aflatoxin biosynthesis, the conversion of versicolorin A and sterigmatocystin was unaffected, but the conversion of versiconal acetate was markedly inhibited. The mutant accumulating versicolorin A incorporated 14C-labeled acetate, averufin, and versiconal acetate into versicolorin A. In the presence of dichlorvos, however, the major conversion product was versiconal acetate. This strongly suggested that dichlorvos inhibited the conversion step of versiconal acetate into versicolorin A. This mutant resumed production of aflatoxin B1 if sterigmatocystin was added to the resting cell cultures, indicating that the mutant was blocked at the enzymatic step catalyzing the conversion of versicolorin A into sterigmatocystin, and as a result was incapable of aflatoxin production. The experimental evidence is thus provided for the involvement and interrelationship of three anthraquinones (averufin, versiconal acetate, and versicolorin A) and a xanthone (sterigmatocystin) in aflatoxin biosynthesis. A pathway for the biosynthesis of aflatoxin B1 is proposed to be: acetate →→→ averufin → versiconal acetate → versicolorin A → sterigmatocystin → aflatoxin B1. 相似文献
998.
Thomas F. Hogan Ernest C. Borden Betty L. Freeberg John Vieau Fang-Yuh Hsieh John Crowley 《Cancer immunology, immunotherapy : CII》1980,10(1):27-31
Summary Candida, mumps, and streptokinase-streptodornase (SKSD) were administered intradermally to 38 healthy adult volunteers at weeks 0, 2, 4–5, and 14 during two separate trials. Frequent, repetitive testing was used to determine (1) whether responses remained stable; (2) the relationship of erythema to induration; and (3) whether results would change when analyzed by different methods of comparing endpoints.When Candida, mumps, and SKSD were first administered, 63%, 76%, and 88% of the subjects responded with 5 mm induration by 48 h. Although little sex difference was noted for mumps and SKSD responses, more men responded to Candida (P=0.001). Erythema and induration were linearly correlated for Candida and SKSD, but the results were variable for mumps. With frequent repetitive testing, the mean induration arising in response to Canadida increased (P=0.001), as did the number of responses >15 mm (P=0.05). Similarly, the mean mumps-induced induration increased (P=0.01), as did the number of responses >10 mm (P=0.05). The mean SKSD-induced induration increased (P=0.08) in the first trial. During the second trial an SKSD overdosage occurred, which produced SKSD-specific anergy lasting for 25 weeks but not affecting Canadida and mumps responses. All enhanced induration responses decreased toward baseline levels during a 10-week rest period. The graded-response method of data analysis was more sensitive than the positive-negative or mean induration methods for detecting significant induration enhancement. Appropriate controls are needed for meaningful data analysis during repetitive skin testing with these antigens. 相似文献
999.
Enzymes of glycogen metabolism and related metabolites in preimplantation mouse embryos 总被引:1,自引:0,他引:1
Preimplantation mouse embryos were individually analyzed for glycogen phosphorylase, P-glucomutase, UDPG, UTP, ATP, and the sum of other nucleotide triphosphates (i.e., GTP + CTP). UDPG changes during starvation and refeeding were also determined. Phosphorylase activity was exceedingly low at the two-cell stage and rose eightfold by the morula stage. P-glucomutase was 2000 times more active than phosphorylase in two-cell embryos and fell progressively to about half the initial level by the eight-cell stage. UDPG was highest in one-cell embryos, fell to less then 20% by the two-cell stage, then recovered to about a 35% level at later stages. The ATP to UTP ratio varied from about 5:1 at the earliest stages to about 3:1 in eight-cell and older embryos. GTP plus CTP was 50% higher than UTP at the one-cell stage but was equal to UTP or lower thereafter. The results combined with earlier data from several laboratories indicate that (1) up to the morula stage the embryo can make glycogen but has difficulty using it because of insufficient glycogen phosphorylase and (2) UDPG and glucose-6-P levels are poorly coordinated, probably due to difficulty (or control) at the UDPG pyrophosphorylase step. 相似文献
1000.
Lee C- Cheng W- Chang M- Su Y- Chen C- Hsieh F- 《Apoptosis : an international journal on programmed cell death》2005,10(4):887-894
Background: To evaluate the influence of hypoxia and molecular events in endothelial and embryonic stem cells.Materials and Methods: Human umbilical vein endothelial cells (HUVECs) and mouse embryoid body (EB) cells were subjected to hypoxic conditions for different time courses. DNA fragmentation assay, quantification of apoptotic cells by TUNEL assay measured by flowcytometry, and Western blot analysis for the molecular events of apoptosis were performed.Results: DNA fragmentation could be identified under hypoxic conditions in HUVECs and mouse EBs. The DNA fragmentation increased when the hypoxic interval was extended.In situ internucleosomal DNA fragmentation-TUNEL assay also found that the percentages of apoptotic cells increased gradually in HUVECs and mouse EBs when the hypoxic interval was extended. Furthermore, the levels of expression of p53 and Bax both increased in hypoxic conditions.Conclusions: Hypoxia increases both HUVEC and mouse EB apoptosis, which is associated with increase in p53/Bax expression. 相似文献