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1.
Polysome and ribosome preparations from normal rat liver and from a series of transplantable rat hepatomas of different growth rates were compared. All the hepatomas had a significantly higher percentage of RNA in a polysome preparation than did the normal liver, and the polysome preparations from the tumors, with the exception of the Dunning hepatoma which has a high lipid content, gave a greater yield of RNA and protein per gram of wet tissue than the liver did. Heavier polysomes were considerably less prevalent in the tumors than in the liver, and the tumors contained a larger proportion of monomer and dimer ribosomes than the liver did. Evidence is presented that the increased monomer and dimer ribosome population of the hepatomas studied is not an artifact of preparation, but represents the true intracellular distribution. Ribosomes from normal liver and Morris 5123-D hepatoma were readily dissociated by 20 min'' treatment with 1.0 mM EDTA, but ribosomes from the Dunning, Novikoff ascites, and McCoy MDAB hepatomas were little affected by such treatment. With higher concentrations of EDTA, the ribosomes from the Novikoff ascites and McCoy MDAB hepatomas broke down and did not form specific subunits as did ribosomes from liver and the Morris 5123-D hepatoma but rather gave rise to a variety of small degradation products. This behavior is ascribed to a higher RNase content of the Novikoff and McCoy MDAB hepatomas. Dunning hepatoma ribosomes were resistant to 4 mM EDTA.  相似文献   

2.
The effect of protein undernutrition on the activity of the smoothendoplasmic reticulum (microsomal) Ca2+-ATPase (SERCA) wasinvestigated. After 12 weeks of ad libitum ingestion of low proteindiet (5% protein), a significant depression (p<0.05) of liver ERCa2+-ATPase activity (68.6% depression) was observed. However,no significant effects on cytochrome P450 activity and relative liverweight were found. It is proposed that low protein diet by inhibitingthe rat liver SERCA activity, might increase the cytosolic free calciumion concentration ([Ca2+]) and promote the development of livertumor. The possible mechanisms of low protein diet induced inhibition ofSERCA activity are highlighted.  相似文献   

3.
Some properties of rat spleen ribonuclease have been studied, and the intracellular distribution of the enzyme and ribonucleic acid have been presented. Spleen ribonuclease exhibits maximal activity at pH 5.8, and although there is some evidence for the presence of an enzyme with an optimum at pH 7.0, it is not conclusive. The enzyme is concentrated primarily in the mitochondrial fraction, but significant quantities occur in the supernatant fluid. The latter contains ribonuclease inhibitor similar to that found in liver. The effects of whole body x-irradiation, magnesium ion, substrate concentration, type of buffer, presence of p-chloromercuriphenylsulfonic acid, deoxycholate, and Triton X-100 on ribonuclease activity are examined.  相似文献   

4.
为了探讨羟基磷灰石纳米粒子(nHAP)对大鼠肝线粒体生物活性的影响,将nHAP直接作用于线粒体,在不同浓度和时间下测定线粒体标志酶琥珀酸脱氢酶(SDH)比活性,并与对照组进行比较。结果显示,当nHAP中水含量在10%以下时,线粒体生物活性未发现改变;当nHAP浓度递增时,在等时间段内,对线粒体SDH比活性呈逐步抑制作用;在不等时间段内,nHAP对线粒体SDH比活性的抑制作用与对照组相比较差异有显著性(p<0.05)。因此,nHAP对线粒体SDH比活性的抑制有浓度和时间的依赖性。  相似文献   

5.
将纯化得到的蛇毒凝血酶(TLE_3、TLE_4),经家兔体内实验表明,2—3凝血酶单位/kg体重剂量能显著地使家兔全血凝血时间缩短1/3—1/2。药后1小时即有促凝作用,以2—4小时凝血(止血)效应最强,12小时已消失。与Holleman, W. H.等自美洲矛头蝮蛇毒中得到的蛇毒凝血酶(Hemocoagulase)相似。经家兔及家犬实验性创伤止血实验表明,对创伤出血有止血作用。  相似文献   

6.
1. In all the concentrations of ether studied (from 0.037 to 7.3 per cent) there is an increase in the rate of respiration of Bacillus subtilis followed by a decrease. 2. In 7.3 per cent ether in tap water there is an extraordinary increase in the output of CO2 (amounting to 50 times the normal). This does not occur when 0.85 per cent NaCl is added, which indicates antagonism between ether and NaCl. 3. Ether is toxic in low concentrations (0.037 to 1.1 per cent) and high concentrations (3.65 to 7.3 per cent) but in intermediate concentrations (1.1 to 3.65 per cent) stimulates growth.  相似文献   

7.
The zonal ultracentrifuge was used to separate the subcellular components of rat liver brei into soluble phase, microsomal, mitochondrial, membranous fragments, and nuclear fractions during a single centrifugation. The centrifuge was run at 10,000 to 30,000 RPM for 15 to 240 minutes, and the rotor contained a 1200 ml sucrose gradient, varying linearly with radius from 17 to 55 per cent sucrose with a "cushion" of 66 per cent sucrose at the rotor edge. The distribution of the mitochondria was determined using cytochrome oxidase as the marker enzyme. An automated assay system for cytochrome oxidase was developed utilizing reduced cytochrome c as substrate, modules of the Technicon Autoanalyzer, and the Beckman DB Spectrophotometer. All of the cytochrome oxidase activity was restricted to a single peak in the gradient, and no activity could be detected in the zones occupied by the microsomes and nuclei. The mitochondrial fraction was isolated from rat liver brei in 0.25 M sucrose by differential centrifugation, and then run in the zonal ultracentrifuge.This fraction behaved in the zonal ultracentrifuge in the same way as mitochondria separated directly from intact brei. Observations of the isolated fractions in the phase contrast microscope indicated that a wide variety of granules was present in the mitochondrial zone in addition to the true mitochondria. Under the conditions employed, the mitochondria were sedimented essentially to their isopycnic position in the gradient at approximately 43.8 per cent sucrose, density 1.20 gm/cc.  相似文献   

8.
In vascular plants, the apical meristem of the shoot normally represents a continuation of growth in the apical meristem of the embryo itself. This is not the case in Arceuthobium. Here the shoot apex of the embryo is rudimentary and eventually dies after infection of the host occurs. The inflorescence of Arceuthobium is, therefore, an adventitious structure originating in the endophytic system rather than from the shoot apex of the seedling. Inflorescence buds arise in either of 2 ways. In some species (A. douglasii and A. americanum), buds first appear as small meristematic protuberances on the outer surface of cortical strands. In other species (A. campylopodum), the buds arise at the ends of short branches. The former, or diffuse, type gives rise to inflorescences along the entire surface of the host branch; in the latter, or condensed, type inflorescences are formed in clusters. Early ontogeny of the inflorescence apex of both types is described. Studies of subsequent growth of the inflorescence apex show 5 well-defined plastochronic stages: (1) maximal area stage; (2) minimal area stage; (3) early post-minimal stage; (4) late post-minimal stage; and (5) pre-maximal stage.  相似文献   

9.
The transfer numbers of the ions of electrolytes in the dried collodion membrane, as determined in a previous paper indirectly from the E.M.F. of concentration chains, can also be determined directly by electrical transfer experiments. It is shown that the difficulties involved in such experiments can be overcome. The transfer numbers obtained by the two methods are in satisfactory agreement. The experimental results obtained in the transfer experiments furnish an additional argument in favor of maintaining the theory that the electromotive effects observed in varying concentrations of different electrolytes with the dried collodion membrane may be referred to differences in the mobilities of the anions and cations within the membrane. As was shown by the method of the previous paper, the transfer number depends largely on concentration. There are some minor discrepancies between the values of the transfer numbers obtained by the two methods which, as yet, cannot be completely explained.  相似文献   

10.
1. The phenomenon of protein racemization is discussed and certain deductions are made in connection with the hypothesis of Dakin to account for this phenomenon and Robertson''s theory of the ionization of proteins. 2. Experimental data are given to show that the electrochemical behavior of racemic casein is not in accord with the deductions which have been drawn from the theory advanced by Robertson. 3. An analysis of the nitrogen groups of racemic casein is given and compared with a similar analysis of normal casein. From these analyses and from the electrochemical equivalent of racemic casein, it is concluded that except for the hydrolysis of amide groups, racemic casein is probably not a degradation product of casein. 4. Considerable evidence is presented against the view that the -COHN- groups take part in the reactions of the protein molecule with acids and with bases.  相似文献   

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12.
阿霉素铁(Ⅲ)配合物与DNA结合作用的研究   总被引:2,自引:0,他引:2  
应用吸收光谱法研究了阿霉素铁(Ⅲ)[ADM·Fe(Ⅲ)]与DNA的结合作用,结果表明ADM·Fe(Ⅲ)作为一个整体嵌入DNA碱基之间形成ADM·Fe(Ⅲ)·DNA三元复合物。应用荧光淬灭法得到了不同Na+浓度下ADM及ADM·Fe(Ⅲ)与DNA结合作用的结合常数(K)、结合位点距离(n)及标准自由能(ΔG),并根据多聚电解质理论将ΔG分解为电荷作用部分(ΔGpe)及非电荷作用部分(ΔGt)。结果表明ADM·Fe(Ⅲ)中铁离子直接参与了与DNA的作用,ADM·Fe(Ⅲ)较ADM更易与DNA结合,且结合更为紧密  相似文献   

13.
  1. The cells of Thiobacillus thiooxidans, which had been in contactwith sulfur or sulfide in air (or CO2-free air), could fix addedCOa very rapidly after replacing air with nitrogen. This fixationis designated as the postoxidative fixation.
  2. "Preoxidation"of the sulfur compounds is mandatory for theoccurrence of thepostoxidative fixation.
  3. The cells which had preliminarilyoxidized sulfide could notshow the CO2-fixation, when theywere placed under an anaerobiccondition in the absence of thesulfur compound.
  4. These results indicate that sulfur compoundsmay have an importantrole as the electron donor for the reductionof CO2, besidestheir role as the substrate of respiration tosecure energyfor the fixation of CO2
(Received March 6, 1962; )  相似文献   

14.
《Free radical research》2013,47(5):277-281
The effect of phorbol-12-myristate-13-acetate (PMA), an activator of protein kinase C (PK-C) on lipid peroxidation (LPO) in rat liver homogenates and microsomes was studied. PMA (10?10 to 10?6M) produced a concentration-dependent inhibition of LPO, which was greatly decreased by polymyxin B (Px B) (an inhibitor of PK-C). The non-active analogue of PMA, 4α-phorbol-12,13-didecanoate (4α-PDD) exerted no inhibitory effect. The adenylate cyclase activator, forskolin (FK) (10?6 M) abolished the inhibitory effect of PMA on LPO. PMA and FK did not inhibit LPO in liposomes. It is suggested that LPO in biomembranes could be regulated by PK-C, whose inhibitory effect might be prevented by CAMP-dependent protein kinases.  相似文献   

15.
In the autotrophic bacterium, Thiobacillus thiooxidans, the oxidation of sulfur is coupled to transfers of phosphate from the medium to the cells. CO2 fixation is coupled to transfers of inorganic phosphate from the cells to the medium and is dependent, in the absence of concomitant sulfur oxidation, upon the amount of phosphate previously taken up during sulfur oxidation. The energy reservoir, which is formed by sulfur oxidation in the absence of CO2 and which can be released for the fixation of CO2 under conditions which do not permit sulfur oxidation, is a phosphorylated compound and the data suggest that the energy is stored in the cell as phosphate bond energy. It is possible to oxidize sulfur at a constant rate for hours in the absence of CO2. The phosphate energy formed during this process is probably released by cell phosphotases. It is possible to inhibit these phosphotases by means of inorganic phosphate and thus to inhibit sulfur oxidation in the absence of CO2. In the presence of CO2, where alternative uses for the phosphate energy are available, the inhibition is relieved. Sulfur oxidation (energy input) is coupled, not to CO2 fixation, but to phosphate esterification. CO2 fixation (energy utilization) is coupled with phosphate release.  相似文献   

16.
小叶章草地生态系统结构与功能的研究Ⅳ能量的固定和分配   总被引:11,自引:0,他引:11  
马克平 《生态学报》1995,15(1):23-31
小叶章草在生态系统年净初级生产力为30579。17kJ/m^2.a,其中地上净初级生产力占37.64%,地下净初级生产力占62.36%。不同植物器官(组分)的能量现存量差异很大,上部根占植物亚系统总能量现存量的54.87%,穗的能量现存量仅占0.03%,其它器官的能量现存量从大到小依次为:茎>叶>根茎>枯落物>下部根茎>死根。不同植物器官(组分)热值含量水平亦存在较大差异,以去灰分热值比较,由大到  相似文献   

17.
18.
1. The flight muscles of blowflies are easily dispersed in appropriate media to form suspensions of myofibrils which are highly suitable for phase contrast observation of the band changes associated with ATP-induced contraction. 2. Fresh myofibrils show a simple band pattern in which the A substance is uniformly distributed throughout the sarcomere, while the pattern characteristic of glycerinated material is identical with that generally regarded as typical of relaxed vertebrate myofibrils (A, I, H, Z, and M bands present). 3. Unrestrained myofibrils of both fresh and glycerinated muscle shorten by not more than about 20 per cent on exposure to ATP. In both cases the A substance migrates during contraction and accumulates in dense bands in the Z region, while material also accumulates in the M region. It is proposed that these dense contraction bands be designated the Cz, and Cm bands respectively. In restrained myofibrils, the I band does not disappear, but the Cz and Cm bands still appear in the presence of ATP. 4. The birefringence of the myofibrils decreases somewhat during contraction, but the shift of A substance does not result in an increase of birefringence in the Cz and Cm bands. It seems therefore that the A substance, if it is oriented parallel with the fibre axis in the relaxed myofibril, must exist in a coiled or folded configuration in the C hands of contracted myofibrils. 5. The fine structure of the flight muscle has been determined from electron microscopic examination of ultrathin sections. The myofibrils are of roughly hexagonal cross-section and consist of a regular single hexagonal array of compound myofilaments the cores of which extend continuously throughout all bands of the sarcomere in all states of contraction or relaxation so far investigated. 6. Each myofilament is joined laterally with its six nearest neighbours by thin filamentous bridges which repeat at regular intervals along the fibre axis and are present in the A, I, and Z, but not in the H or M bands. When stained with PTA, the myofilaments display a compound structure. In the A band, a lightly staining medullary region about 40 A in diameter is surrounded by a densely staining cortex, the over-all diameter of the myofilament being about 120 A. This thick cortex is absent in the I and H bands, but a thinner cortex is often visible. 7. It is suggested that the basic structure is a longitudinally continuous framework of F actin filaments, which are linked periodically by the lateral bridges (possibly tropomyosin). The A substance is free under certain conditions to migrate to the Z bands to form the Cz bands. The material forming the Cm bands possibly represents another component of the A substance. The results do not clearly indicate whether myosin is confined to the A bands or distributed throughout the sarcomere.  相似文献   

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