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1.
羚牛(Budorcas taxicolor)部分脏器特点的观察 总被引:2,自引:2,他引:0
本文对2只羚牛的雌性生殖器官及肝、肾、脾等脏器进行了形态描述,并与黄牛及羊的相应器官进行了比较,为探讨羚牛的分类地位提供了解剖学资料。 相似文献
2.
R.N. Shukla Surjeet Singh Nibhriti Das Madhulika Baijal G.G. Sanwal 《Phytochemistry》1973,12(5):979-985
Considerable variations exist in the content of glucose, fructose, sucrose, starch and protein and in the activities of enzymes involved in carbohydrate metabolism between different parts of the banana plant (Musa paradisiaca). Sucrose synthetase is present in the highest concentration in rootstock and fruit pulp, and sucrose phosphate synthetase in the pseudostem. The highest ratio of the activity of sucrose phosphate synthetase to sucrose synthetase is found in leaves. Acid invertase is present in leaves, leaf-sheath and fruit pulp and is not demonstrable in rootstock and pseudostem. Neutral invertase activity is high in pseudostem and leaf-sheath. Starch phosphorylase is largely concentrated in fruit pulp and rootstock. The maximum activity of ATP:d-phosphoglucose (ADPG) pyrophosphorylase is found in rootstock. β-Amylase is not demonstrable in rootstock and is largely concentrated in leaf-sheath. Hexokinase is most active in rootstock and the lowest in leaves. Acid phosphatase and alkaline phosphatase activity is highest in fruit pulp and pseudostem. Glucosephosphate isomerase is most active in the rootstock and lowest in the leaves. 相似文献
3.
Walker RP Chen ZH Johnson KE Famiani F Tecsi L Leegood RC 《Journal of experimental botany》2001,52(356):565-576
To understand many aspects of the metabolism of complex plant structures such as leaves, fruit and roots it is important to understand how metabolic processes are compartmentalized between tissues. The aim of this article is to show how immunohistochemistry, in conjunction with biochemical and physiological studies, is useful in understanding both the function of an enzyme in a tissue and metabolic processes occurring in plant tissues. This is illustrated by two examples. Firstly, the use of immunohistochemisty in the localization of amino acids in plant tissues is described. Secondly, the use of immunohistochemistry in understanding the function of an enzyme in a tissue and the metabolic processes occurring within the tissue is described. To illustrate this the example of phosophoenolpyruvate carboxykinase (PEPCK), an enzyme which is present in many plant tissues in which its function is unknown, is used. Evidence is provided that PEPCK may play a role in pH regulation in tissues active in the metabolism of nitrogen. 相似文献
4.
5.
Cytoplasmic localization of the ORF2 protein of hepatitis E virus is dependent on its ability to undergo retrotranslocation from the endoplasmic reticulum
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Hepatitis E virus (HEV) is a positive-strand RNA virus that is prevalent in much of the developing world. ORF2 is the major capsid protein of HEV. Although ORF2 is an N-linked glycoprotein, it is abundantly located in the cytoplasm in addition to having membrane and surface localization. The mechanism by which ORF2 protein obtains access to the cytoplasm is unknown. In this report, we prove that initially all ORF2 protein is present in the endoplasmic reticulum and a fraction of it becomes retrotranslocated to the cytoplasm. The ability of ORF2 to be retrotranslocated is dependent on its glycosylation status and follows the canonical dislocation pathway. However, in contrast to general substrates of the dislocation pathway, retrotranslocated ORF2 protein is not a substrate of the 26S proteasome complex and is readily detectable in the cytoplasm in the absence of any protease inhibitor, suggesting that the retrotranslocated protein is stable in the cytoplasm. This study thus defines the pathway by which ORF2 obtains access to the cytoplasm. 相似文献
6.
DNA synthesis after ultraviolet irradiation is low in wild type toluene-treated cells. The level of repair incorporation is greater in strains deficient in DNA polymerase I. The low level of repair synthesis is attributable to the concerted action of DNA polymerase I and polynucleotide ligase. Repair synthesis is stimulated by blocking ligase activity with the addition of nicotinamide mononucleotide (NMN) or the use of a ligase temperature-sensitive mutant. NMN stimulation is specific for DNA polymerase I-mediated repair synthesis, as it is absent in isogenic strains deficient in the polymerase function or the 5' leads to 3' exonuclease function associated with DNA polymerase I. DNA synthesis that is stimulated by NMN is proportional to the ultraviolet exposure at low doses, nonconservative in nature, and is dependent on the uvrA gene product but is independent of the recA gene product. These criteria place this synthesis in the excision repair pathway. The NMN-stimulated repair synthesis requires ATP and is N-ethylmaleimide-resistant. The use of NMN provides a direct means for evaluating the involvement of DNA polymerase I in excision repair. 相似文献
7.
Jason R. Treberg Margaret E. Brosnan Malcolm Watford John T. Brosnan 《Advances in enzyme regulation》2010,50(1):34-43
GDH is readily reversible in vitro, but the situation in vivo is more complex. There is very strong evidence that this enzyme catalyses a close-to-equilibrium reaction in the liver, which is appropriate for its role in balancing the nitrogenous inputs (ammonia and aspartate) required for urea synthesis. In many other tissues it is likely that GDH is poised in the deamination direction. It is clear that GDH is not close-to-equilibrium in pancreatic β-cells, but is poised in the deamination direction. We suggest that the issue of the reversibility of GDH in the kidney needs to be reappraised. The HI/HA syndrome is brought about by gain-of-function mutations in which the ability of GTP to inhibit GDH is reduced, or even eliminated. Increased GDH activity in β-cells of HI/HA patients increases glutamate oxidation, which raises the ATP/ADP ratio and stimulates insulin secretion. The origin of the hyperammonemia of the HI/HA syndrome is not clear. However, the close-to-equilibrium nature of hepatic GDH precludes the liver as the source of the elevated ammonia levels. Future work should address the extra-hepatic origin of the hyperammonemia. The identification of this source (or sources) of ammonia is critical for the design of therapies, or metabolic approaches, that can reduce its concentration. 相似文献
8.
We show that even in the complete absence of potential energies among the atoms in a protein-aqueous solution system, there is a physical factor that favors the folded state of the protein. It is a gain in the translational entropy (TE) of water originating from the translational movement of water molecules. An elaborate statistical-mechanical theory is employed to analyze the TE of water in which a protein or peptide with a prescribed conformation is immersed. It is shown that if the number of residues is sufficiently large, the TE gain is powerful enough to compete with the conformational-entropy loss upon folding. For protein G we have tested over 100 compact conformations generated by a computer simulation with the all-atom potentials as well as the native structure. A significant finding is that the largest TE is attained in the native structure. The translational movement of water molecules is quite effective in achieving the tight packing in the interior of a natural protein. These results are true only when the solvent is water whose molecular size is the smallest among the ordinary liquids in nature. 相似文献
9.
D S Thaler E Sampson I Siddiqi S M Rosenberg L C Thomason F W Stahl M M Stahl 《Génome》1989,31(1):53-67
RecBCD enzyme is centrally important in homologous recombination in Escherichia coli and is the source of ExoV activity. Null alleles of either the recB or the recC genes, which encode the B and C subunits, respectively, manifest no recombination and none of the nuclease functions characteristic of the holoenzyme. Loss of the D subunit, by a recD mutation, likewise results in loss of ExoV activity. However, mutants lacking the D subunit are competent for homologous recombination. We report that the distribution of exchanges along the chromosome of Red-Gam-phage lambda is strikingly altered by recD null mutations in the host. When lambda DNA replication is blocked, recombination in recD mutant strains is high near lambda's right end. In contrast, recombination in isogenic recD+ strains is approximately uniform along lambda unless the lambda chromosome contains a chi sequence. Recombination in recD mutant strains is focused toward the site of action of a type II restriction enzyme acting in vivo on lambda. The distribution of exchanges in isogenic recD+ strains is scarcely altered by the restriction enzyme (unless the phage contains an otherwise silent chi). The distribution of exchanges in recD mutants is strongly affected by lambda DNA replication. The distribution of exchanges on lambda growing in rec+ cells is not influenced by DNA replication. The exchange distribution along lambda in recD mutant cells is independent of chi in a variety of conditions. Recombination in rec+ cells is chi influenced. Recombination in recD mutants depends on recC function, occurs in strains deleted for rac prophage, and is independent of recJ, which is known to be required for lambda recombination via the RecF pathway. We entertain two models for recombination in recD mutants: (i) recombination in recD mutants may proceed via double-chain break--repair, as it does in lambda's Red pathway and E. coli's RecE pathway; (ii) the RecBC enzyme, missing its D subunit, is equivalent to the wild-type, RecBCD, enzyme after that enzyme has been activated by a chi sequence. 相似文献
10.
红腹锦鸡血细胞的光镜和扫描电镜观察 总被引:11,自引:3,他引:8
为了探讨红腹锦鸡(Chrysolophus pictus)血细胞的形态特征,为生理学研究提供生物学基础资料,利用光镜和扫描电镜观察了红腹锦鸡血细胞的形态特征。结果表明,红腹锦鸡红细胞呈椭圆形或扁圆形,表面光滑,具核;白细胞为球形,体大,淋巴细胞表面有绒毛状突起,嗜中性粒细胞核一般分2~5叶,嗜酸性粒细胞核一般分2叶,嗜碱性粒细胞核分2~3叶,单核细胞表面粗糙不平,核大,呈肾形或圆形;凝血细胞呈球形或不规则形。 相似文献
11.
The expression pattern of the receptor tyrosine kinase gene EphB3 was examined during the early stages of chick embryogenesis, and is described in this report. In the gastrula, EphB3 is expressed in epiblast cells adjacent to and entering the anterior portion of the primitive streak; expression is extinguished once cells have ingressed. At headfold stages, EphB3 is strongly transcribed in the floor of the foregut and in anterior lateral endoderm, and is expressed in the subjacent cardiogenic mesoderm. EphB3 is transiently expressed in the lateral ectoderm, neural tube, and neural crest during these stages. Later neural expression is localized to the mesencephalon. In the somitic mesoderm, EphB3 is initially expressed in the sclerotome, but later is expressed predominantly in the dermatome. Prominent expression is also detected in the developing heart, liver, posterior ventral limb bud mesenchyme, pharyngeal arches, and head mesenchyme. 相似文献
12.
The ubiquitous presence of exopolygalacturonase in maize suggests a fundamental cellular function for this enzyme 总被引:3,自引:0,他引:3
Manuel Dubald Abdellah Barakate Paul Mandaron Régis Mache 《The Plant journal : for cell and molecular biology》1993,4(5):781-791
Exopolygalacturonase (exoPG) is a pectin-degrading enzyme abundant in maize pollen. Using immunochemistry and in situ hybridization it is shown that in addition to its presence in pollen, exoPG is also present in sporophytic tissues, such as the tapetum and mesophyll cells. The enzyme is located in the cytoplasm of pollen and of some mesophyll cells. In other mesophyll cells, the tapetum and the pollen tube, exoPG is located in the cell wall. The measurement of enzyme activity shows that exoPG is ubiquitous in the vegetative organs. These results suggest a general function for exoPG in cell wall edification or degradation. ExoPG is encoded by a closely related multigene family. The regulation of the expression of one of the exoPG genes was analyzed in transgenic tobacco. Reporter GUS activity was detected in anthers, seeds and stems but not in leaves or roots of transgenic plants. This strongly suggests that the ubiquitous presence of exoPG in maize is the result of the expression of different exoPG genes. 相似文献
13.
The small molecular weight RNAs of the HeLa cell have been located in specific subcellular fractions. SnA is located in the nucleolus and is partially bonded to nucleolar 28S RNA. SnD, the most abundant of the small nuclear RNAs, is partially released from the nucleus when the nuclear preparation is briefly warmed. SnF is released from the nuclei when chromatin is digested with the micrococcal nuclease and not when pancreatic DNAase is used. The remainder of the small nuclear species remain in the nucleus following the digestion of chromatin and are concluded to be elements of the “nuclear skeleton.” SnK is found predominantly in the cytoplasm, but migrates quantitatively to the nuclear fraction in the presence of high levels of actinomycin D. ScL is totally cytoplasmic and is partially bound to cell membranes. It is the 7S RNA found in oncornavirus virions. All the small nuclear RNAs appear initially in the cytoplasmic fraction before fixation in the nucleus. Two short-lived cytoplasmic species behave kinetically as precursors to the stable nuclear RNAs. 相似文献
14.
Control of glucose metabolism in the perinatal period 总被引:1,自引:0,他引:1
C T Jones 《Journal of developmental physiology》1991,15(2):81-89
The central importance of glucose as a fuel for energy metabolism and growth of the fetus is clear as is the role of insulin in coordinating its utilisation by many fetal tissues. What is less clear is the qunatitative nature of the interaction between the fetus and placenta in organising glucose metabolism. Increasingly there is evidence that the fetus coordinates some of the supply of glucose to the placenta and that this is particularly important when uterine blood flow is reduced. It is unclear how this is regulated, but substrate cycles of glucose and lactate appear to make a significant contribution to carbohydrate metabolism in fetus and placenta. Another area as yet unresolved in the control of fetal glucose metabolism is the coordination of the changes that occur around the time of birth. Notable of these is the activation of glycogen mobilisation and of glucose synthesis and changes in the setting of glucose regulatory mechanism. These are briefly reviewed. 相似文献
15.
R Werner 《Comp. Biochem. Physiol. C, Comp. Pharmacol. Toxicol.》1988,90(2):445-450
1. Cortisol is the major corticosteroid in the guinea-pig plasma; cortisone is detected in minor concentrations. 2. An increase in the plasma cortisol level is observed during acute cold exposure. 3. After application of metopirone-ditartrate the standard metabolic rate is depressed significantly at thermoneutrality. 4. In metopirone-treated guinea-pigs the cold-induced increase in heat production is depressed by 47% concomitant with a marked drop in body temperature. 5. It is concluded that the formation of cortisol is essential for regulatory heat production induced by acute cold exposure in the guinea-pig. 相似文献
16.
扬子鳄视觉器官组织学研究 总被引:11,自引:0,他引:11
本文用光镜和电镜研究了扬子鳄(Alligator sinensis)的组织学,同时测量了其眼球的一些光学参数.扬子鳄眼球呈扁圆球形,角膜径与球径的比值为1:1.44;晶状体与角膜的比值为1:1.40。角膜内具鲍氏膜;虹膜内的括约肌、睫状体内的睫状肌均属横纹肌,视细胞椭圆体内线粒体嵴突与线粒体长轴相平行,这与报道的其它鳄类不同。虹膜内未见扩瞳肌纤维,角膜缘缺巩膜小骨片,晶状体环垫薄,因而其视觉调节能力仍然很弱。视网膜中视细胞由视杆细胞、单锥细胞、双锥细胞组成,其中以视杆细胞占多数。视细胞与神经节细胞核比值平均为2.5:1,表明扬子鳄的组织结构与其弱光视觉相适应。 相似文献
17.
Martin HM Moore KP Bosmans E Davies S Burroughs AK Dhillon AP Tosh D Harrison R 《Free radical biology & medicine》2004,37(8):1214-1223
Xanthine oxidoreductase (XOR) is a widely distributed enzyme, involved in the metabolism of purines, which generates superoxide and is thought to be involved in free radical-generated tissue injury. It is present at high concentrations in the liver, from where it may be released during liver injury into the circulation, binding to vascular endothelium and causing vascular dysfunction. The cellular localization of the enzyme, essential to understanding its function, is, however, still debated. The present study has used a highly specific mouse monoclonal antibody to define the cellular distribution of XOR in normal and cirrhotic human liver. As shown previously, XOR is present in hepatocytes. However, the novel finding of this study is that XOR is present in bile duct epithelial cells, where it is concentrated toward the luminal surface. Moreover, in liver disease, proliferating bile ducts are also strongly positive for XOR. These findings suggest that the enzyme is secreted into bile, and this was confirmed by analysis of human and rat bile. Xanthine oxidase activity was 10 to 20-fold higher in liver tissue obtained from patients with liver disease, than in healthy liver. We conclude that XOR is expressed primarily in hepatocytes, but is also present in bile duct epithelial cells and is secreted into bile. Its role in bile is unknown but it may be involved in innate immunity of the bowel muscosa. 相似文献
18.
Neurophysiological mechanisms underlying face processing within and beyond the temporal cortical visual areas. 总被引:4,自引:0,他引:4
E T Rolls 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》1992,335(1273):11-20; discussion 20-1
The ways in which information about faces is represented and stored in the temporal lobe visual areas of primates, as shown by recordings from single neurons in macaques, are considered. Some neurons that respond primarily to faces are found in the cortex in the anterior part of the superior temporal sulcus (in which neurons are especially likely to be tuned to facial expression and to face movement involved in gesture), and in the TE areas more ventrally forming the inferior temporal gyrus (in which neurons are more likely to have responses related to the identity of faces). Quantitative studies of the responses of the neurons that respond differently to the faces of different individuals show that information about the identity of the individual is represented by the responses of a population of neurons, that is, ensemble encoding rather than 'grandmother cell' encoding is used. It is argued that this type of tuning is a delicate compromise between very fine tuning, which has the advantage of low interference in neuronal network operations but the disadvantage of losing the useful properties (such as generalization, completion and graceful degradation) of storage in neuronal networks, and broad tuning, which has the advantage of allowing these properties of neuronal networks to be realized but the disadvantage of leading to interference between the different memories stored in an associative network. There is evidence that the responses of some of these neurons are altered by experience so that new stimuli become incorporated in the network. It is shown that the representation that is built in temporal cortical areas shows considerable invariance for size, contrast, spatial frequency and translation. Thus the representation is in a form which is particularly useful for storage and as an output from the visual system. It is also shown that one of the representations that is built is object based, which is suitable for recognition and as an input to associative memory, and that another is viewer centred, which is appropriate for conveying information about gesture. Ways are considered in which such cortical representations might be built by competitive self-organization aided by back projections in the multi-stage cortical processing hierarchy which has convergence from stage to stage. 相似文献
19.
鼎湖山顶级森林生态系统水文要素时空规律 总被引:14,自引:4,他引:10
运用连续7a(1993~1999)的水文观测资料,对南亚热带顶级生态系统鼎湖山季风常绿阔叶林集水区水文要素时空规律进行分析,得到如下一些主要结论:(1)鼎湖山多年平均降水量为1910mm,湿季降水量占年降水量80%,干季仅占20%。6月份的降水量最大,1月份最小。(2)季风常绿阔叶林冠层截留率为31.8%,湿季的截留量占全年截留量的66.7%,截留量最大值和最小值所在的月份分别为7和1月份。各月的截留率差异很大,截留量大的月份,截留率较低;截留量小的月份,截留率较高。(3)季风常绿阔叶林集水区多年平均总径流量953.0mm,总径流系数49.9%,其中地表径流量为252.3mm,地表径流系数13.2%;地表径流与降水量之间存在二次抛物线型回归关系,与降水强度的关系不大,这说明季风常绿阔叶林的产流形式是是蓄满产流。(4)季风常绿阔叶林多年平均蒸散948.2mm,占同期降水量的49.7%;蒸散力1031.4mm,年蒸散系数为0.92,蒸散月变化规律较降水量的月变化规律有所滞后。(5)系统贮水量的月变化很大,2~8月份,系统处于蓄水阶段;9月份至翌年1月份,系统处于失水阶段。蓄水和失水的最大值分别出现在湿季和干季的第一个月,即4月份和10月份。(6)集水区多年平均水量总输入2129.9mm,实际输入1910mm(降水量),其中219.9mm的水量输入是由系统贮水量变化而产生。支出的总水量2129.9mm,实际支出1901.3mm(径流和蒸散量),其中228.6mm的水量支出是由系统贮水量变化引起的。 相似文献
20.
1. beta-Hydroxy-beta-methyl[3-(14)C]glutaryl-CoA is efficiently incorporated into rubber on incubation with Hevea brasiliensis latex, and the incorporation is diminished in the presence of unlabelled mevalonate. beta-Hydroxy-beta-methylglutaric acid is not utilized for rubber synthesis, but inhibits the formation of rubber from beta-hydroxy-beta-methylglutaryl-CoA. 2. The incorporation of beta-hydroxy-beta-methylglutaryl-CoA into rubber is stimulated equally by NADP(+) and NADPH and less so by NAD(+) and NADH. ATP is slightly stimulatory and CoA is inhibitory. 3. beta-Hydroxy-beta-methylglutaryl-CoA reductase is concentrated in the sediment (bottom fraction) formed by centrifuging latex at low speed and the enzyme is unstable in the absence of cysteine or GSH. The formation of NADPH takes place in the latex serum. 4. There is a marked seasonal variation in the extent of beta-hydroxy-beta-methylglutaryl-CoA incorporation into rubber in latex, but mevalonate incorporation is relatively constant. This observation, together with the finding that beta-hydroxy-beta-methylglutaryl-CoA reduction is the rate-limiting step in the formation of rubber from beta-hydroxy-beta-methylglutaryl-CoA, suggests that the conversion of beta-hydroxy-beta-methylglutaryl-CoA into mevalonate is of importance in the regulation of rubber synthesis. 5. Evidence suggesting that beta-hydroxy-beta-methylglutaryl-CoA lyase is present in H. brasiliensis latex has been obtained. 相似文献