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91.
The roles of plasticity and evolutionary change in shaping gene expression variation in natural populations of extremophile fish 下载免费PDF全文
92.
R Jalleh DJ Torpy 《The Clinical biochemist. Reviews / Australian Association of Clinical Biochemists》2021,42(1):17
Direct measurement of the nonapeptide vasopressin has been limited by analyte instability ex vivo and in vivo rapid degradation, low serum concentrations requiring a sensitive assay and inherent secretory pulsatility. Copeptin is a 39 amino acid glycopeptide cleavage product of vasopressin synthesis with high stability, providing a marker of vasopressin secretion. Copeptin measurement has applications in diagnosis of diabetes insipidus and other diseases with altered vasopressin secretion. This review summarises our current understanding of serum copeptin measurement in diabetes insipidus and possible future applications of copeptin assays. As vasopressin is a stress hormone, there is emerging evidence on the use of copeptin for diagnosis and prognostication of disorders such as syndrome of inappropriate anti-diuretic hormone secretion, diabetes mellitus, critical illness, stroke, cardiovascular disease, respiratory disease, renal disease and thermal stress. Copeptin concentration measurement is likely to improve the diagnostic reliability of diabetes insipidus and, as a marker of stress, may have diagnostic or prognostic utility in specific clinical circumstances. Further studies are needed to determine if goal-directed therapy using plasma copeptin concentrations may improve patient outcomes. 相似文献
93.
Evolution at the tip and base of the X chromosome in an African population of Drosophila melanogaster 总被引:1,自引:0,他引:1
Hitchhiking effects of advantageous mutations have been invoked to explain
reduced polymorphism in regions of low crossing-over in Drosophila. Besides
reducing DNA heterozygosity, hitchhiking effects should produce strong
linkage disequilibrium and a frequency spectrum skewed toward an excess of
rare polymorphisms (compared to the neutral expectation). We measured DNA
polymorphism in a Zimbabwe population of D. melanogaster at three loci,
yellow, achaete, and suppressor of forked, located in regions of reduced
crossing-over. Similar to previously published surveys of these genomic
regions in other populations, we observed low levels of nucleotide
variability. However, the frequency spectrum was compatible with a neutral
model, and there was abundant evidence for recombination in the history of
the yellow and ac genes. Thus, some aspects of the data cannot be accounted
for by a simple hitchhiking model. An alternative hypothesis, background
selection, might be compatible with the observed patterns of linkage
disequilibrium and the frequency spectrum. However, this model cannot
account for the observed reduction in nucleotide heterozygosity. Thus,
there is currently no satisfactory theoretical model for the data from the
tip and base of the X chromosome in D. melanogaster.
相似文献
94.
Oligogalacturonic acids (OGAs), derived from plant cell wall pectin, have
been implicated in a number of signal transduction pathways involved in
growth, development and defense responses of higher plants. This study
investigates the size range of OGAs capable of inducing ethylene synthesis
in tomato plants, and demonstrates that in contrast with many other
effects, only short chain OGAs are active. Oligomers across a range of DP
from 2-15 were separated and purified to homogeneity by QAE-Sephadex anion
exchange chromatography using a novel elution system. The OGAs were applied
to tomato plants and assayed for their ability to induce ethylene gas
release and changes in steady state levels of mRNA encoding the ethylene
forming enzyme aminocyclopropane-1-carboxylic acid oxidase (ACO). The study
demonstrated that only OGAs in the size range of DP4-6 were active both in
eliciting ACO expression and in the production of ethylene.
相似文献
95.
96.
A change in twist of actin provides the force for the extension of the acrosomal process in limulus sperm: the false-discharge reaction 总被引:6,自引:5,他引:1 下载免费PDF全文
One of the most spectacular motions is the generation of the acrosomal process in the limulus sperm. On contact with the egg, the sperm generates a 60-mum-long process that literally drills its way through the jelly surrounding the egg. This irresversible reaction takes only a few seconds. We suggested earlier that this motion is driven by a change in twist of the actin filaments comprising the acrosomal process. In this paper we analyze the so-called false discharge, a reversible reaction, in which the acrosomal filament bundle extends laterally from the base of the sperm and not anteriorly from the apex. Unlike the true discharge, which is straight, the false discharge is helical. Before extension, the filament bundle is coiled about the base of the sperm. In the coil, the bundle is not smoothly bent but consists of arms (straight segments) and elbows (corners) so that the coil looks like a 14-sided polygon. The extension of the false discharge works as follows: starting at the base of the bundle, the filaments change their twist which concomitantly changes the orientations of the elbows relative to each other; that is, in the coil, the elbows all like in a common plane, but after the change in twist, the plane of each elbow is rotated to be perpendicular to that of its neighbors. This change transforms the bundle from a compact coil into an extended left- handed helix. Because the basal end of the bundle is unconstrained, the extension is lateral. The true discharge works the same way but starts at the apical end of the bundle. The apical end, however, is constrained by its passage through the nuclear canal, which directs the extention anteriorly. Unlike the false discharge, during the true discharge the elbows are melted out, making the reaction irreversible. This study shows that rapid movement can be regenerated by actin without myosin and gives us insight into the molecular mechanism. 相似文献
97.
The catalytic activity of the LDH-isoenzymes depends on their tetrameric structure. Low pH or other denaturants leads to dissociation into monomers and to the loss of the specific activity. After removal of the denaturing conditions reassociation and reactivation occur spontaneously. Neither NADH nor NAD+ shows a significant effect on the reactivation. We have isolated two different peptides which isoenzyme specifically inhibit the reactivation of dissociated LDH. Inhibition was abolished by treating with proteases. Additionally, NAD+ and NADH were found to be antagonists of the inhibitors. The heart-type enzyme-inhibitor system is especially susceptible for NADH whereas NAD+ affects the inhibition only slightly. The muscle-type system shows the opposite behavior, e.g., the completely inhibited system can be fully reactivated by NAD+ but not by NADH. These findings together with first kinetic studies suggest a possible specific regulatory function of these peptides. 相似文献
98.
The binding and processing of plasminogen by Balb/c 3T3 and SV3T3 cells was studied using 125I-labeled canine plasminogen. Throughout a 3-day period, 125I-plasminogen in the incubation medium bound to the cells and was degraded, first to intermediate-sized macromolecules that were the same size as the large (74,600-dalton) and small (25,000-dalton) chains of active plasmin, and to smaller fragments including 3-iodo-L-tyrosine. Binding to SV3T3 cells was independent of the protease-dependent morphological change (PDMC)1 characteristic of these and many other transformed cells. The SV3T3, and to a somewhat lesser extent, the 3T3 cells, both accumulated and released into the incubation medium 3-iodo-L-tyrosine, a terminal lysozymal digestion product. The results of a sublethal cell-surface trypsinization assay suggest that the cell-associated plasminogen was primarily bound to the surfaces of the 3T3 and SV3T3 cells while the macromolecular degradation products including active plasmin were inside the cells. The rate of 125I plasminogen degradation exhibited by SV3T3 cells was approximately two times greater than that of 3T3 cells, which presumably reflects differences in endocytosis or lysosomal hydrolysis, or both. The rates were unaffected by addition of pancreatic or soybean trypsin inhibitor sufficient to inhibit PDMC. In the incubation medium, plasminogen was activated to plasmin by SV3T3, but not by 3T3 cells. However, 95–100% of plasmin covalently bound to a 47,000-dalton canine serum component, which could be dissociated from plasmin by hydroxylamine: 95–100% of the plasmin was inactive to reaction with DF32P. Thus the serum component is a plasmin inhibitor. The plasmin-containing complex in the medium had an apparent molecular weight of 212,000. Under denaturing conditions, the complex dissociated into two covalently modified plasmin-containing species of 153,000 and 127,000 daltons. In addition to forming a complex with a serum component, the plasmin is cleaved into two small fragments (~10,000 and 12,000 daltons) by as-yet uncharacterized serum factors. 相似文献
99.
Normal and tumorous human mammary tissues were incubated in vitro with [7α-3H] dehydroepiandrosterone and [7α-3H] dehydroepiandrosterone sulphate. Tritium-labelled 7α-hydroxy dehydroepiandrosterone was identified as a principal metabolite from four of the five studies with normal tissue and all seven studies with tumorous tissue. 相似文献
100.
A radioimmunoassay for plasma 3 beta, 7 alpha-dihydroxy-5-androsten-17-one (7 alpha-hydroxy DHA) has been developed using anti-sera raised against 3 beta, 7 alpha-dihydroxy-5-androstene-17 beta-carboxyl-bovine serum albumin conjugate and [1, 2 (n) - 3H] 7 alpha-hydroxy DHA as the radioligand. Significant cross reactivity was found with 3 beta, 7 alpha-dihydroxy-5-pregnen-20-one (44%), 3 beta, 7 beta-dihydroxy-5-androsten-17-one (6%), 3 beta, 6 beta-dihydroxy-4-androsten-17-one (2.5%), 3 beta-hydroxy-5-androsten-17-one (DHA, 2%), 3 beta, 7 beta-dihydroxy-5-pregnen-20-one (2%) and 7 alpha-hydroxy-4-androstene-3, 20-dione (1%). 7 alpha-Hydroxy DHA was extracted from plasma and separated from cross-reacting factors using alumina micro-columns. The separation of bound and free steroid was achieved using dextran-coated charcoal. The concentration of 7 alpha-hydroxy DHA in the plasma of breast cancer patients was significantly lower than the concentrations in the plasma of normal women, hospitalized women suffering from non-endocrine diseases and patients with benign breast disease. The decrease in the concentration of 7 alpha-hydroxy DHA in the plasma of pregnant women was not significant. 相似文献