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1.
Enzymology of DNA in replication in prokaryotes 总被引:10,自引:0,他引:10
K J Marians 《CRC critical reviews in biochemistry》1984,17(2):153-215
This review stresses recent developments in the in vitro study of DNA replication in prokaryotes. New insights into the enzymological mechanisms of initiation and elongation of leading and lagging strand DNA synthesis in ongoing studies are emphasized. Data from newly developed systems, such as those replicating oriC containing DNA or which are dependent on the lambda, O, and P proteins, are presented and the information compared to existing mechanisms. Evidence bearing on the coupling of DNA synthesis on both parental strands through protein-protein interactions and on the turnover of the elongation systems are analyzed. The structure of replication origins, and how their tertiary structure affects recognition and interaction with the various replication proteins is discussed. 相似文献
2.
The effect of neutralizing endogenous follicle stimulating hormone (FSH) or luteinizing hormone (LH) with specific antisera on the in vivo and in vitro synthesis of estrogen in the ovary of cycling hamster was studied. Neutralization of FSH or LH on proestrus resulted in a reduction in the estradiol concentration of the ovary on diestrus-2 and next proestrus, suggesting an impairment in follicular development. Injection of FSH antiserum at 0900 h of diestrus-2 significantly reduced the ovarian estradiol concentration within 6--7 h. Further, these ovaries on incubation with testosterone (T) in vitro at 1600 h of the same day or the next day synthesized significantly lower amounts of estradiol, compared to corresponding control ovaries. Although testosterone itself, in the absence of endogenous FSH, could stimulate estrogen synthesis to some extent, FSH had to be supplemented with T to restore estrogen synthesis to the level seen in control ovaries incubated with T. Lack of FSH thus appeared to affect the aromatization step in the estrogen biosynthetic pathway in the ovary of hamster on diestrus-2. In contrast to this, FSH antiserum given on the morning of proestrus had no effect on the in vivo and in vitro synthesis of estrogen, when examined 6--7 h later. The results suggest that there could be a difference in the need for FSH at different times of the cycle. Neutralization of LH either on diestrus-2 or proestrus resulted in a drastic reduction in estradiol concentration of the ovary. This block was at the level of androgen synthesis, since supplementing testerone alone in vitro could stimulate estrogen synthesis to a more or less similar extent as in the ovaries of control hamsters. 相似文献
3.
Lopez-Delgado H. Jimenez-Casas M. Scott I.M. 《Plant Cell, Tissue and Organ Culture》1998,54(3):145-152
Acetylsalicylic acid was investigated as an alternative medium supplement to mannitol for slow-growth in vitro storage of
potato microplants. At 8°C, culture in the presence of either 100 μM acetylsalicylic acid or 4% mannitolretarded microplant
stem growth, and required intervals between subcultures ranged from 8 to over 12 months, depending on the genotype. Several
media were tested for recovery of clones from slow-growth storage, with similar efficiences of recovery achieved for microplants
from either mannitol or acetylsalicylic acid media. Prolonged culture on acetylsalicylic acid had no adverse effects on the
yield of minitubers on plantlets transferred to glasshouse cultivation. At 18°C also, intervals between subcultures could
be prolonged to 5.5–6 months by culture on either mannitol or acetylsalicylic acid media. Microplants cultured on acetylsalicylic
acid did not exhibit the frequent phenotypic abnormalities found in microplants on mannitol medium.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
4.
In our previous study we have demonstrated that treatment of endometrial explants with LH increased 13,14-dihydro-15-ketoprostaglandin F(2alpha) (PGFM) accumulation in pigs. This was particularly visible on Days 14-16 of the estrous cycle. Action of gonadotropin in porcine endometrium appears to be mediated by LH/hCG receptors whose number is dependent on the day of the estrous cycle. In the current study i.v. infusion (1 hour) of hCG (200 IU) performed on Days 10 (n=4) and 12-14 (n=4) of the porcine estrous cycle did not affect plasma PGFM (ng/ml+/-SEM) concentrations. In contrast, administration of hCG on Days 15-17 produced, depending on plasma PGFM level before the infusion period, three different types of response: I. plasma PGFM surge of amplitude 0.62+/-0.15 was observed when the mean basal pre-infusion PGFM plasma level was 0.23+/-0.05 (n=6 gilts); II. the delayed PGFM surge of amplitude 0.62+/-0.15 was determined when basal pre-infusion PGFM level was 0.80+/-0.20 (n=6); and III. lack of PGFM response to hCG was found when basal pre-infusion PGFM level was 1.09+/-0.61 (n=6). Concentrations of plasma PGFM before and after saline infusion did not differ on Days 12-14 and 16 of the estrous cycle. In the next experiment blood samples were collected every 1 hour on Days 12-19 of the estrous cycle to determine concentrations of LH, PGFM and progesterone in four gilts. In particular gilts, plasma peaks of LH closely preceded surges of PGFM in 72.7, 84.6, 75.0 and 66.6 percent, respectively. The highest PGFM surges followed a decline in plasma progesterone concentration. We conclude that the increased PGF(2alpha) metabolite production after hCG infusion during the late luteal phase of the estrous cycle as well as the relationship between plasma LH and PGFM peaks suggest the LH involvement in the elevation of endometrial PGF(2alpha) secretion in pigs, and, in consequence, induction of luteolysis. 相似文献
5.
Survival of replacement cultures of Mucor species in oxygenat 10 atm was markedly affected by the carbon source; culturesreplaced on glucose media survived for a much shorter periodthan cultures on water while 1 per cent ethanol increased thesurvival time. This effect of carbon source on survival wascorrelated with changes in catalase activity; in the presenceof glucose and other carbohydrates, catalase activity decreasedwhereas on 1 per cent ethanol a large increase in catalase activityoccurred which was maintained for several days. An increasein catalase activity also occurred on methanol, pyruvate, glycerol,and formate. Induced changes in peroxidase activity were similarto those shown by catalase but the activity of three other enzymesdecreased in hyperbaric oxygen on all media. 相似文献
6.
V P Zhalko-Titarenko A V Grigor'ev V M Bondarenko V K Koval'chuk 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1988,(9):28-33
The dependence of the invasive action of Salmonella typhimurium in mice on the aggregation of microbial cells has been studied in vivo, as well as in vitro on explanted intestinal tissue. The aggregation of salmonellae on kaolin grains has been found to lead to an increase in the level of adhesion of salmonellae to the intestinal mucosa of mice in vitro, to the accelerated course of infection in mice and their death and to the increased contamination of the spleen. The data obtained in these experiments age indicative of the possibility of the adverse influence of some sorbents on the course of the infectious process and confirm the concept advanced by the authors on the major importance of the surface concentration of salmonellae on the mucous membrane for the effectiveness of contamination. 相似文献
7.
Sorbitol content was determined in the digestive gland of freshwater snail (Viviparus viviparus L.) in different seasons and in a short-term experiment on the water temperature decrease and on intoxication with cadmium
chloride. In the model experiments, changes in activities of enzymes involved in sorbitol metabolism (acid phosphatases, sorbitol
dehydrogenase, and aldose reductase) were also studied. Sorbitol was accumulated by the snail in response to the temperature
decrease (as a cryoprotectant) and under conditions of acute intoxication (as a probable metabolic regulator or a nonspecific
protective factor). However, the mechanisms of this accumulation are different: on cold adaptation sorbitol is produced as
a result of reduction of glucose under the influence of aldose reductase, and on intoxication sorbitol is mainly produced
from fructose under the influence of sorbitol dehydrogenase. Pathways of the sorbitol accumulation and its re-involvement
into metabolism are not always the same, and this might be a mechanism for regulation of carbohydrate metabolism (at the initial
stage of glycolysis) on adaptation to unfavorable factors of the environment. 相似文献
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In facultatively sexual species, lineages that reproduce asexually for a period of time can accumulate mutations that reduce their ability to undergo sexual reproduction when sex is favorable. We propagated Saccharomyces cerevisiae asexually for approximately 800 generations, after which we measured the change in sexual fitness, measured as the proportion of asci observed in sporulation medium. The sporulation rate in cultures propagated asexually at small population size declined by 8%, on average, over this time period, indicating that the majority of mutations that affect sporulation rate are deleterious. Interestingly, the sporulation rate in cultures propagated asexually at large population size improved by 11%, on average, indicating that selection on asexual function effectively eliminated most of the mutations deleterious to sporulation ability. These results suggest that pleiotropy between mutations' effects on asexual fitness and sexual fitness was predominantly positive, at least for the mutations accumulated in this experimental evolution study. A positive correlation between growth rate and sporulation rate among lines also provided evidence for positive pleiotropy. These results demonstrate that, at least under certain circumstances, selection acting on asexual fitness can help to maintain sexual function. 相似文献
10.
Diet of raccoon dogs in summer in the Finnish archipelago 总被引:1,自引:0,他引:1
The diet of raccoon dogs in summer was examined in the Finnish archipelago and compared with their diet on the mainland. Faeces were collected from latrines in the outer archipelago and the inhabited islands in May-July 1998 and 1999. Remains of waterfowl, especially those of female cider, occurred frequently in the faeces of raccoon dogs on the uninhabited islands, but less frequently on the inhabited islands and only occasionally on the mainland. Since many female eider died of disease during the summer in 1998 and 1999. and white-tailed eagles arc known to prey on brooding eider, it is probable that raccoon dogs did not themselves kill all the eider they consumed. Even if they did, they would only take a few percent of female eider population each year. It is thus improbable that raccoon dogs affect the size of the eider population in the Finnish archipelago. Frogs, reptiles, shrews and carrion occurred frequently in the diet on the mainland, but only occasionally in the outer archipelago. It is possible that raccoon dogs have decimated frog populations on small islands, as they are easy prey and occur frequently in the diet of raccoon dogs on the mainland. Small rodents are important prey for raccoon dogs on the mainland and on inhabited islands, but less important in the outer archipelago in early summer. 相似文献
11.
The equine embryonic vesicle is mobile on Days 12-14 (Day 0 = ovulation), when it is approximately 9-15 mm in diameter. Movement from one uterine horn to another occurs, on average, approximately 0.5 times per hour. Mobility ceases (fixation) on Days 15-17. Transrectal color Doppler ultrasonography was used to study the relationship of embryo mobility (experiment 1) and fixation (experiment 2) to endometrial vascular perfusion. In experiment 1, mares were bred and examined daily from Day 1 to Day 16 and were assigned, retrospectively, to a group in which an embryo was detected (pregnant mares; n = 16) or not detected (n = 8) by Day 12. Endometrial vascularity (scored 1-4, for none to maximal, respectively) did not differ on Days 1-8 between groups or between the sides with and without the corpus luteum. Endometrial vascularity scores were higher (P < 0.05) on Days 12-16 in both horns of pregnant mares compared to mares with no embryo. In pregnant mares, the scores increased (P < 0.05) between Day 10 and Day 12 in the horn with the embryo and were higher (P < 0.05) than scores in the opposite horn on Days 12-15. In experiment 2, 14 pregnant mares were examined from Day 13 to 6 days after fixation. Endometrial vascularity scores and number of colored pixels per cross-section of endometrium were greater (P < 0.05) in the endometrium surrounding the fixed vesicle than in the middle portion of the horn of fixation. Results supported the hypothesis that transient changes in endometrial vascular perfusion accompany the embryonic vesicle as the vesicle changes location during embryo mobility. 相似文献
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Ovsiannikov VI Berezina TP 《Rossi?skii fiziologicheski? zhurnal imeni I.M. Sechenova / Rossi?skaia akademiia nauk》2008,94(6):689-699
In experiments on unanaesthetized rabbits myoelectric activity (contractile activity index) of proximal (postpyloric) and distal sites of duodenum, and proximal part of jejunum was studied under stress induced by fastening a rabbit to a table in supine position. In both sites of duodenum, the stress impact induced a short-time decrease of contractile activity which was followed by its increase that exceeded the initial level. In the proximal part ofjejunum, the increase of contractile activity took place only during the second part of stress response. The strengthening of the contractile activity of the proximal part of duodenum was preserved after muscarinic or nicotinic cholinoceptor blockage, and after beta-receptor blockage. It was concluded that the contractile response of the proximal part of duodenum did not result from the contribution of central or local neurogenic mechanism, including excitatory cholinergic one, but was humoral in origin. The strengthening of the contractile activity of the distal part of duodenum and proximal part ofjejunum was abolished by muscarinic cholinoceptor and beta-receptor blockage, and resulted from the action of circulating catecholamines on the excitatory beta-adrenoceptor, localized on the cholinergic neurones of the enteric nervous system. 相似文献
16.
Thyroid hormones are known to stimulate in vivo the synthesis of several liver proteins. In order to determine their role in the regulation of important hepatic proteins at the cell level, the effect of T3 on the induction of the glucoregulatory enzyme phosphoenolpyruvate carboxykinase (PEPck) was investigated in cultured hepatocytes. The cells were isolated from adult hypothyroid rats and exposed to a chemically defined medium, devoid of serum supplement and hormone-free over a period of 48 h. Addition of T3 to the medium had only a minor effect on PEPck induction. Dibutyryladenosine 3',5'-monophosphate (Bt2cAMP) or epinephrine provoked significant increase in PEPck synthesis within 4-6 h. Simultaneous addition of T3 was found significantly to promote the Bt2cAMP-mediated enzyme induction. Physiological concentrations of T3 (10 pM to 1 nM) were found to be effective in enhancing this cAMP-mediated signal. Exposure of the cells to T3 for only 90 min, 16 h prior to addition of Bt2cAMP was nearly as effective as continuous exposure to T3 in enhancing the cAMP-effect on PEPck synthesis. In contrast, no effect of T3 on the Bt2cAMP-induced tyrosine-aminotransferase activity could be detected. It is concluded that the role of T3 on the cAMP-elicited PEPck synthesis is selective, rapid, primarily permissive and significant within the physiological range of the hormone. In addition, these data indicate that such hepatocyte cultures prepared from hypothyroid rats are ideally suited to the analysis of the regulatory role of thyroid hormones on specific gene expression. 相似文献
17.
细胞分裂素对植物衰老的延缓作用 总被引:5,自引:0,他引:5
细胞分裂素是一类重要的植物激素,它可在一定程度上延缓植物的衰老。主要从3个方面综述了细胞分裂素与植物衰老之间的关系,即:(1)植物衰老过程中内源细胞分裂素含量变化;(2)外源细胞分裂素的影响;(3)转入与细胞分裂素的合成、降解相关的基因对植物衰老产生的影响。此外,还从细胞分裂素与糖、与脂质氧化反应以及与其它植物激素的关系方面探讨了细胞分裂素在延缓植物衰老中的作用机理。 相似文献
18.
M Candau B Bertrand J Fioramonti 《Comptes rendus des séances de la Société de biologie et de ses filiales》1978,172(3):554-559
Fiber digestibility of two diets (the first based on alfalfa dried, the second based on beet-pulp dried) with the same level of crude fiber and crude protein was measured on rabbits of 6, 7, 11, 13 and 17 weeks old. The age has no significative effect on digestibility (dry matter, organic matter, crude fiber) of the two experimental diets. The quantity of cellulose and hemicellulose digested was greater in rabbits on the pulp diet. Independantly of the diet hemicellulose is more digestible than cellulose. Expediency of use other analytical test than crude fiber in the nutritional requirements of rabbits is discussed. 相似文献
19.
槲皮素药理作用研究进展 总被引:101,自引:0,他引:101
本文概括了国内外近20年来有关槲皮素的药理研究,综述了槲皮素抗肿瘤,抗炎,抗血小板聚集,扩张冠脉等作用,并从分子生物学角度初步探讨了槲皮素抗病毒的机理。 相似文献