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1.
Summary The pattern of intercellular connections between germ line cells has been studied in follicles of the mutantdicephalic (dic), which possess nurse cell clusters at both poles. Staining of follicles with a fluorescent rhodamine conjugate of phalloidin reveals ring canals and cell membranes and thus allows us to reconstruct the spatial organization of the follicle. Each germ line cell can be identified by the pattern of cell-cell connections which reflect the mitotic history of individual cells in the 16-cell cluster. The results indicate that in both wild-type anddicephalic cystocyte clusters one of the two cells with four ring canals normally becomes the pro-oocyte. However, in some follicles (dicephalic and wild-type) oocytes were found with fewer or more than four ring canals. Indic follicles, one or several nurse cells may become disconnected from the other cells during oocyte growth at stage 9–10. Such disconnected cells cannot later on empty their cytoplasm into the oocyte. This, in turn, might be of consequence for the determination of axial polarity of the embryo. 相似文献
2.
Pampatheres are extinct, large‐bodied cingulates, which share morphological characters with both armadillos and glyptodonts but are considered to be more closely related to the latter. The osteoderm histology of six pampathere taxa was examined and compared to the histology of other cingulate osteoderms. This study investigates the development and functional adaptation of pampathere osteoderms as well as the phylogenetic relationships of the Pampatheriidae within the Cingulata. We found that pampathere osteoderms share a uniform histological organization based on a basic diploe‐like structure. After initial stages of intramembranous growth, metaplastic ossification, that is, the direct incorporation and mineralization of pre‐existing protein fibers, plays an important role in osteoderm development and provides information on various kinds of soft tissue otherwise not preserved. The latest stages of osteoderm growth are dominated by periosteal bone formation especially in the superficial cortex. Movable band osteoderms show regular arrangements of incorporated fibers that may increase the resistance of particularly weak areas against strain. The histological composition of pampathere osteoderms is plesiomorphic in its basic structure but shows a number of derived features. A unique array of Sharpey's fibers that are incorporated into the bone matrix at sutured osteoderm margins is interpreted as a synapomorphy of pampatheres. The arrangement of dermal fibers in the deep and superficial cortexes supports the close relationship between pampatheres and glyptodonts. J. Morphol., 2012. © 2011 Wiley Periodicals, Inc. 相似文献
3.
5-Bromouracil is dehalogenated in the presence of bisulfite buffers to yield uracil which subsequently adds bisulfite to form 5,6-dihydrouracil-6-sulfonate. Presumably, 5-bromo-5,6-dihydrouracil-6-sulfonate is an intermediate in uracil formation. Kinetic data indicate that the disappearance of 5-bromouracil in the presence of bisulfite buffers is second order with respect to total bisulfite concentration, thus indicating the participation of 2 moles of either sulfite or bisulfite in the overall reaction, Iodometric titrations of total bisulfite combined with spectral analysis of the various pyrimidine and dihydropyrimidine species present indicate that, in addition to the total bisulfite required to form 5,6-dihydrouracil-6-sulfonate, an additional mole of sulfite is consumed per mole of 5-bromouracil dehalogenated. These data combined with the finding that sulfate is generated during dehalogenation are indicative of a pathway for the dehalogenation of the intermediate 5-bromo-5,6-dihydro-uracil-6-sulfonate which involves the attack of sulfite either directly or via an intervening molecule of water to yield uracil. Subsequent reactions of halogen-containing intermediates yield sulfate and bromide as final products of the reaction. 相似文献
4.
Polarity as a criterion in protein design 总被引:6,自引:0,他引:6
Hypothetical proteins can be tested computationally by determining whether or not the designed sequence-structure pair has the characteristics of a typical globular protein. We have developed such a test by deriving quantities with approximately constant value for all globular proteins, based on empirical analysis of the exposed and buried surfaces of 128 structurally known proteins. The characteristic quantities that best appear to segregate badly designed or deliberately misfolded proteins from their properly folded natural relatives are the polar fraction of side chains on the protein surface and, independently, in the protein interior. Three of the seven hypothetical structures tested here can be rejected as having too many polar side-chain groups in the interior or too few on the protein surface. In addition, a recently designed nutritional protein is identified as being very much unlike globular proteins. These database-derived characteristic quantities are useful in screening designed proteins prior to experiment and may be useful in screening experimentally determined (X-ray, NMR) protein structures for possible errors. 相似文献
5.
Ultrastructural localization of WGA,RCA I,LFA and SBA binding sites in the seven-day-old mouse embryo 总被引:1,自引:0,他引:1
Summary Transglutaminases are Ca2+-dependent intra-and extracellular enzymes catalyzing the cross-linking between proteins and/or polyamines, thereby eliciting
divergent physiological effects such as fibrin clot stabilization or hair follicle cross-linking. A secretory transglutaminase
(EC 2.3.2.13) was isolated from the coagulating gland of the rat. The protein is highly glycosylated. A fraction purified
to homogeneity was used as an antigen to raise polyclonal antibodies in rabbits. These antibodies were used to identify the
secretion sites of the protein within the male accessory sex glands as well as to study the immunological relationships of
the respective antigen within different organs of different species. In the rat, the coagulating gland and likewise the dorsal
prostate gave a positive immunoreaction. In the guinea pig, a closely related protein was detected in the anterior prostate.
No cross-reactivity was found with membrane-bound transglutaminase from liver, erythrocytes or blood clotting factor XIIIa.
The intraluminal secretion of the aforementioned glands was only weakly stained. No secretory granules were observed in the
glandular epithelium but instead bleb-like structures reminiscent of apocrine secretion. A slight background stain of the
epithelium remained even in castrated animals where secretion is largely suppressed. The background stain is attributed to
a tissue-type, membrane-bound, non-secretory transglutaminase that is not androgen dependent, but instead synthesized only
after androgen deprivation. 相似文献
6.
W. M. Van der Krieken A. F. Croes G. W. M. Barendse G. J. Wullems 《Physiologia plantarum》1988,74(1):113-118
Benzyladenine (BA) was found to regulate the number of flower buds regenerated in vitro from pedicel tissue of tobacco. Flower bud induction was particularly sensitive to BA levels in the range of 0.45 to 1.0 μ M , where a two-fold increase in concentration caused a threefold rise in the number of buds. When tissues were fed radioactive BA for 24h, only 9–12% of the counts were recovered in the original compound. The rest was present in metabolites, tentatively identified as the mono-, di- and triribotides, 7- and 9-glucosides and 9-riboside of BA. The amount of growth regulator taken up and the quantities of BA and its metabolites in the explants were all linearly related to the concentration of the medium. The internal BA concentration was ca 60% of the level in the medium after 24 h. When the concentration in the medium was raised, relatively more BA remained in the non-conjugated form. However, this change in the equilibrium between BA and the conjugates is too small to account for the steep rise in the curve representing concentration vs effect between 0.45 and 1.0 μ M . 相似文献
7.
8.
9.
The rate constants for the reversible addition of protons and sulfite to the 5,6 double bond of cytidine and 3-methylcytidine have been spectrophotometrically measured under conditions (25°C, μ = 1.0
) where the deamination of 5,6-dihydrocytidine-6-sulfonate is minimal. Both the addition and the elimination of sulfite from the ring system are subject to general catalysis of proton transfer. For the reaction in either direction, plots of the pseudo-firstorder rate constants against increasing buffer concentration are biphasic and indicative of at least a two-step reaction pathway with both steps being subject to general acid-base catalysis. Kinetic hydrogen-deuterium isotope effects were measured for both buffer-catalyzed steps of sulfite elimination from 3-methyl-5,6-dihydrocytidine-6-sulfonate and sulfite addition to 3-methylcytidine. Both H2O and D2O were used as solvent. For both the addition and the elimination of SO32− values of k2H/k2D were 6.3–7.1 and 2.3–2.6 at low and high imidazole buffer concentration, respectively. The large isotope effects values in the range of 6–7 can be attributed to rate-determining proton transfer to carbon-5 of the cytidine ring system. The smaller values are more likely caused by proton transfer to a electronegative atom such as the oxygen on carbon-2 of the cytidine ring. The equilibrium constants for bisulfite buffer addition to 3-methylcytidine and cytidine at 25°C, μ = 1.0
, pH 7.2, are 10.2 and 1.3
−1, respectively. 相似文献
10.
Development of flower buds in thin-layer cultures of floral stalk tissue from tobacco: Role of hormones in different stages 总被引:4,自引:0,他引:4
The in vitro development of flower buds was studied on tissue explants of epidermis and subepidermal cortex from the flower stalks of Nicotiana tabacum L. cv. Samsun. The number of flower buds formed depended mainly on cytokinin concentration. Auxin acted as a modifier in a complex way. In early development, NAA at 1 μ M decreased the number of buds initiated and delayed bud emergence. At a later stage, auxin promoted bud outgrowth at the same concentration. Optimal results were obtained when explants were first incubated at low auxin concentration for 3–5 days and subsequently transferred to an elevated auxin level. Physiological processes that lead to flower bud initiation start very soon after the onset of incubation. This was inferred from experiments whereby explants were first cultured at an inductive cytokinin concentration and then transferred to a non-inductive hormone level. 相似文献