共查询到20条相似文献,搜索用时 281 毫秒
1.
Johan Zwaan 《Developmental biology》1975,44(2):306-312
Aphakia, an autosomal recessive single gene mutation in the mouse, seriously affects the development of the ocular lens. Up to advanced stages of lens invagination morphogenesis proceeds normally. In the late lens cup and early lens vesicle stage, however, the epithelium of the lens rudiment becomes disorganized and the lumen of the vesicle fills up with rounded cells, apparently released from the epithelium. The lens stalk persists frequently. Probably as a consequence of the aphakic state other parts of the eye secondarily become abnormal.Immunofluorescent studies were done on embryonic normal and aphakia eyes with antisera against adult mouse crystallins. In the normal embryo the first positive reactions were found in the late lens cup stage ( days of gestation). By Day 12 all cells of the lens vesicle were brightly fluorescent. A day later the cells of the posterior wall, now lens fibers, had elongated sufficiently to obliterate the lumen of the vesicle. The entire organ was highly fluorescent, indicating that all of its cells contained large amounts of crystallins. The mutant lens, studied over the same time span, showed no reaction at all. The most likely explanation is, that the multiple structural genes, which normally must be involved in the production of the crystallins, are not expressed up to this time in the mutant.The combination of morphological and biochemical defects suggests that the gene involved in the mutation somehow functions in the control of lens differentiation. 相似文献
2.
Glutamine synthetase activity was estimated in the chick cerebral hemispheres, optic lobes and cerebellum between the 1st and the 30th day of postnatal growth. Glutamine synthetase activity is higher in the cerebellum than in the cerebral hemispheres and lowest in the optic lobes at 1 day after hatching; at 30 days after hatching, it is the same in the optic lobes and in the cerebellum and lowest in the cerebral hemispheres. The great increase of glutamine synthetase activity between the 1st and the 4th day after hatching corresponds to the appearance of the heterogeneity of the chick brain glutamate metabolism. The glutamine synthetase activity is inhibited by MSO at a concentration of 100 mg kg ?1 at values of 87, 90 and 89 % in cerebral hemispheres, optic lobes and cerebellum of 1, 2 and 4-day-old chicks. The enzyme inhibition is less pronounced and reaches values of about 25 and 75 % for 1 and 10 mM MSO concentrations respectively in the three brain areas of the 1 to 4-day-old chick and values slightly lower in the 30-day-old chick brain. 相似文献
3.
E Van Deusen 《Developmental biology》1973,34(1):135-158
The phenotype of axolotls (Ambystoma mexicanum) homozygous for the mutant gene e (“eyeless”) is different from normal in that (1) no optic vesicles develop in embryos, (2) larvae from posthatching onward are darker than normal white larvae, and (3) fully grown animals are sterile.Experiments reported here show that eyelessness in embryos results from a direct effect of the gene on presumptive forebrain ectoderm; not on the mesoderm that induces the ectoderm to form eyes. Homotopic grafts of normal presumptive ectoderm on blastula hosts differentiated complete eyes, but reciprocally grafted embryos were always eyeless. Similarly, grafts of either or normal presumptive prechordal mesoderm into normal hosts gave normal eyes, but in the mutant hosts no eyes developed. Thus the e gene affects only the ectodermal component of the inductive system for eye formation.Genetically eyeless (pigmented) cells, when interspersed prior to gastrulation among genetically eyed (albino) cells in the eye preprimordium, are induced to form clones of pigmented retinal epithelium in the albino host eye.The sterility of larvae appears also to be due to a direct effect of the e gene on the ectodermal (neural plate) primordium of the hypothalamus. Grafts of normal cells which included the hypothalamic, but not the optic or anterior pituitary primordia, always restored fertility to recipients.The mutant pigmentation phenotype was demonstrated to be a consequence of eyelessness and, therefore, an indirect effect of the gene. The pigment pattern of normal embryos from which both optic vesicles were removed resembles that of the mutants. In addition, implantation of a single full-sized, functional eye was able to restore the normal pigmentation, but not fertility, to recipients. 相似文献
4.
The formation of the vertebrate optic cup is a morphogenetic event initiated after the optic vesicle contacts the overlying surface/pre-lens ectoderm. Placodes form in both the optic neuroepithelium and lens ectoderm. Subsequently, both placodes invaginate to form the definitive optic cup and lens, respectively. We examined the role of the lens tissue in inducing and/or maintaining optic cup invagination in ovo. Lens tissue was surgically removed at various stages of development, from pre-lens ectoderm stages to invaginating lens placode. Removal of the pre-lens ectoderm resulted in persistent optic vesicles that initiated neural retinal differentiation but failed to invaginate. In striking contrast, ablation of the lens placode gave rise to optic vesicles that underwent invagination and formed the optic cup. The results suggest that: (1) the optic vesicle neuroepithelium requires a temporally specific association with pre-lens ectoderm in order to undergo optic cup morphogenesis; and (2) the optic cup can form in the absence of lens formation. If ectopic BMP is added, a neural retina does not develop and optic cup morphogenesis fails, although lens formation appears normal. FGF-induced neural retina differentiation in the absence of the pre-lens ectoderm is not sufficient to create an optic cup. We hypothesize the presence of a signal coming from the pre-lens ectoderm that induces the optic vesicle to form an optic cup. 相似文献
5.
Ultrastructural evidence indicates that Xenopus retinal ganglion cell axons differentiate early, between stages 28 and 32. Light microscope studies indicated the presence of argryophilic material in the ventral retina and optic stalk of early embryos. Ultrastructural analysis of this region confirmed the presence of axons in the stalk and interstices of ventral retinal cells. Axons containing aligned microtubules and neurofilaments and elongated mitochondria with a paucity of other cell inclusions are found with increasing frequency in the ventral retina from stages 28 through . Central and dorsal regions of the retinas examined show little or no evidence of axons. A discrete, small bundle of axons is found in the optic stalk of stage 28 embryos and by stage the number of axons in bundles has increased, suggesting early fasciculation. Between stages 28 and (± 12 hr) extracellular space surrounding early axons diminishes and processes from neuroretinal cells in contact with axons surround developing axon bundles. The evidence presented suggests that axon initiation occurs in stages much earlier than previously reported. Other investigators have failed to detect ganglion cell differentiation prior to stage 32 possibly because they examined regions of the retina with few axons. Thus, experiments which rotate the retina in the orbit may have to be reevaluated since regenerating axons may use previously established pathways to organize and “home in” on tectal target cells. 相似文献
6.
7.
C D Stout 《Journal of molecular biology》1978,126(1):105-108
Two closely related crystal forms of dimeric cytochrome c5 from Azotobacter rinelandii have been grown. The crystals belong to space groups (C2 with ; and C1 (a centered triclinic cell) with , α = 87 ° 20′, β = 96 ° 40′ and γ = 90 ° 0′. In C2 the 24,000 molecular weight dimer lies on a Crystallographic 2-fold axis; in C1 the entire dimer occupies the asymmetric unit. 相似文献
8.
The partial purification of from pig lens has been achieved by treatment with deoxycholate followed by density gradient centrifugation. The specific activity of the final preparation, ranging from 300 to 500 nmol/h per mg protein, is increased approx. 100-fold compared to the homogenate. A parallel increase in activity is also observed. Sodium dodecyl sulfate (SDS) gel electrophoresis reveals six major protein bands, one of which is the 93 kDa α subunit of which can be phosphorylated by reaction with [γ-32P]ATP. A second band contains a glycoprotein which displays an apparent molecular weight of 51 000 and thus appears to be the β subunit of the enzyme. The enzyme is sensitive to ouabain with the for and inhibition being 1.2 and 1.3 μM, respectively. Several agents which inhibit from other tissues such as oligomycin, Ca2+, vanadate, , (PCMBS) and 5,5′-dithiobis-(2-nitrobenzoic acid) (DTNB) also inhibit the lens enzyme. Monovalent cations other than K+ are partially effective in activating the ()-ATPase and activities. The K+ congeners were relatively more effective in supporting compared to activity. Other kinetic properties of the lens enzyme are also comparable to those of the enzyme from other tissues. Utilizing the partially purified membrane bound enzyme, discontinuities in Arrhenius plots of activity, activity and fluoresence polarization of the fluidity probe, 1,6-diphenyl-1,3,5-hexatriene (DPH), are observed near the physiological temperature of lens. The possible significance of these observations for the mechanism of cataract formation are discussed. 相似文献
9.
R J Siezen 《Journal of molecular biology》1974,90(1):103-113
Helix pomatia α-hemocyanin dissociates within minutes into -size and -size molecules, on increase of pH in the alkaline region.The rate and final state of reassociation of -size and -size molecules have been studied, by turbidity measurements and ultracentrifugation, on lowering of pH or on the addition of calcium ions.Reassociation of molecules proceeds in two phases, with half-times in the order of minutes and one hour, respectively. The slow phase is linked to the disappearance of transitory intermediates, presumably dimers and tetramers of -size molecules.A hysteresis is observed in the final state of pH-dependent and Ca2+-dependent dissociation-reassociation.Reassociation of -size molecules depends on the initial (isomeric) state of these molecules. The F(fast sedimenting)--size molecules reassociate almost completely to whole molecules, whereas the S(slow sedimenting)-form does not reassociate at all. 相似文献
10.
S Friedman 《Biochemical and biophysical research communications》1979,89(4):1328-1333
5-Azacytidine, when added to growing K12, causes a decrease in DNA methylation assayed . This decrease is greater when DNA is used as substrate than when calf thymus DNA is used. The decrease in activity is not due to the inhibition of protein synthesis caused by this drug, since neither chloramphenicol nor rifampin causes a decrease in enzyme activity. The effect is specific for the DNA(cytosine-5)methylase; the methylation of adenine is not affected. The concentration of drug that inhibits the DNA methylase by 50% is the same concentration that inhibits cell growth by 50%. 相似文献
11.
Ana María Marchionatti Beatriz L. Caputto R. Caputto 《Neurochemistry international》1984,6(2):259-263
In contrast with previous findings of the labeling of the glycosidic moieties of the gangliosides and glycoproteins in chickens injected with , the labeling of the ganglion cell layer and optic tectum proteins of chicks exposed to light after an intraocular injection of [3H]proline showed no differences with those of their counterpart chickens that remained in darkness. The same failure in finding a difference was met when the cytosolic or the particulate proteins or the acid soluble fraction in the retina were compared.Cycloheximide and puromycin inhibited the labeling of retina and optic tectum proteins, gangliosides and glycoproteins in both illumination conditions. Since the labelings in the optic tectum appeared more inhibited than those in the retina ganglion cell layer it was concluded that cycloheximide and puromycin, besides the synthesis of those compounds, also inhibit their axonal transport.On the basis of these contrasting results the working hypothesis is advanced that light stimulation enhances the activity of the Golgi apparatus but not (or less) that of the polyribosomes. 相似文献
12.
2-Acetamido-2-deoxy-3-O-(D-2-propionyl-L-alanine)-D-glucopyranose () and 2-acetamido-2-deoxy-3-O-(D-2-propionyl-L-alanyl-D-isoglutamine)-D-glucopyranose () have been synthesized by condensation of benzyl 2-acetamido-4,6-O-benzylidene-3-O-(D-1-carboxyethyl)-2-deoxy-β-D-glucopyranoside () respectively with the L-alanine derivative and the dipeptide , followed by debenzylidenation and hydrogenolysis. Compound is adjuvant active, whereas is inactive, so that is the smallest adjuvant active structure for the time being. 相似文献
13.
Cooperativity in ligand binding: a new graphic analysis. 总被引:16,自引:0,他引:16
When analyzing binding of ligands to macromolecules, the existence of site-site interactions complicates a straightforward interpretation of the binding parameters obtained through classical analytical methods, such as the Scatchard plot. For describing site-site interactions, we propose a new parameter, the of the receptor sites, , calculated as . Plotting as a function of fractional occupancy (), reveals that: (1) at very low occupancy a limiting high is obtained (e) (“empty sites” conformation); (2) when the fraction of sites filled increases above a certain threshold, begins to fall due to increasing site-site interactions until (3) a limiting low (f) is obtained (“filled sites” conformation). This method has been successfully applied to the negative cooperativity of insulin receptors. 相似文献
14.
E.C. Hatchikian M. Bruschi N. Forget M. Scandellari 《Biochemical and biophysical research communications》1982,109(4):1316-1323
A ferredoxin has been isolated from the methanogenic organism (strain Fusaro). The protein appears to be constituted by two identical subunits of molecular weight approx. 6000 daltons. The UV-visible spectrum of the protein is characterized by two broad absorption peaks centered at 410 and 300 nm and an absorbance ratio . The molar extinction coefficients at 410 and 300 nm are 36,500 and 45,625 M?1 cm?1, respectively. The amino acid compsition of ferredoxin shows a preponderance of acidic residues and lacks five amino acids. The protein contains 8 cysteine residues and approx. 7 iron atoms and 7–8 acid-labile sulfide groups per molecule which are indicative of the presence of two iron-sulfur clusters in the molecule. The N-terminal sequence shows a high degree of homology with the sequences of ferredoxins from and ferredoxin functions as an electron carrier in the pyruvate dehydrogenase system. Its possible role in a variety of electron transfer reactions is discussed. 相似文献
15.
G.E. Breitwieser 《生物化学与生物物理学报:生物膜》1982,689(3):457-463
(1) A membrane fraction enriched in (EC 3.6.1.3) was obtained from optic ganglia of the squid (Loligo pealei) by density gradient fractionation of membranes followed by treatment with either SDS or Brij-58. The resulting membrane had an specific activity of approx. 2 units/mg and was ouabain-sensitive. (2) The had a for ATP of and a pH optimum of 7.0. It was inhibited by ouabain with a of . (3) Optimum monovalent cation concentrations were: 240 mM NaCl, 60 mM KCl, tested with . (4) The Mg2+ dependence of hydrolysis varied with the absolute ATP concentration. At 3 mM ATP, the for Mg2+ was , and at 6 mM ATP, the was . High levels of Mg2+ caused inhibition of hydrolysis. (5) The interactions of Na+ and K+ were examined over a range of conditions. K+ levels caused modulations in the Na+ dependence in the range of 1–150 mM. (6) The prepared from squid optic ganglion displays properties similar to those of the sodium pump in injected nerves. 相似文献
16.
The replication defective transducing phage λp3 carries a portion of the operon in the 2 region of the lambda phage. This operon segment contains the promoter, the operator, and the β-galactosidase gene, but does not contain the repressor gene. The gene can be expressed from both the inserted promoter and the phage promoter. When strain 594 (?, +) or JC6256 (Δ) is infected by λp3 in the absence of additional cyclic AMP, β-galactosidase synthesis is shown to be expressed from the phage promoter. When 594 (λ+) or JC6256 (λ+) is infected by λp3 in the presence of additional cyclic AMP and IPTG, β-galactosidase synthesis is shown to be expressed from the inserted promoter.The ability to separate the phage promoter from the inserted promoter for β-galactosidase expression will simplify the interpretation whenever λp5 is used. 相似文献
17.
The epididymis of adult rats metabolize 3H-testosterone by experiments . Thirty minutes after the injection of 100 μCi 3H-testosterone, some 10 per cent of the total radioactivity of the epididymis was found in the water-soluble fraction, whereas 90 per cent was found in the ether soluble fraction (free steroids). The free steroids were examined further and the following androgenic metabolites identified: (17β-hydroxy-4-androsten-3-one) 8, 9%, (4-androstene-3, 17-dione, 2,7%, (5α-androstane-3, 17-dione) 6,5%, (17β-hydroxy-5α-androstan-3-one) 47, 2%, (5α-androstane-3β, 17β-diol) 4, 4%, (5α-androstane-3α,17β-diol) 20, 8% and (3α-hydroxy-5α-androstan-3-one) 3,4%. The relative amount of each metabolite is given in per cent of total radioactivity in the ether soluble fraction. 相似文献
18.
We have shown previously that the synthesis of the lower molecular weight polypeptides of δ-crystallin is differentially reduced and the intracellular ratio is markedly increased in the 15-day-old embryonic chick lens cultured for 3 hr without the vitreous body or in the presence of ouabain. Here we demonstrate that neither δ-crystallin synthesis nor cation concentration is affected in the cultured, vitreous-free 6-day-old embryonic chick lens unless it is treated with ouabain. These results show that the alteration in δ-crystallin synthesis promoted by removing the vitreous body of the embryonic cultured lens is a stage-specific phenomenon, and are consistent with our previous correlation between the ratio of synthesis of the δ-crystallin polypeptides and the intracellular concentration of electrolytes. 相似文献
19.
E J Gabbay R DeStefano C S Baxter 《Biochemical and biophysical research communications》1973,51(4):1083-1089
Proton magnetic resonance (pmr), ultraviolet absorption, induced circular dichroism (CD), and viscometric evidence is presented which show that reporter molecules and bind to DNA via an intercalation process. Preliminary kinetic studies show that the DNA· complex forms rapidly (i.e., <1 msec), whereas the DNA· complex forms at a considerably slower rate (). The kinetic results, and the steric requirements for intercalation of can be explained on the basis of a dynamic structure of DNA. 相似文献
20.
V B Valenty J D Wos A P Lobo W B Lawson 《Biochemical and biophysical research communications》1979,88(4):1375-1381
Thrombin is rapidly inactivated by affinity labeling with 5-acyloxyoxazoles (). The reaction with 2-phenyl-4-(3-N-nitroguanidinopropyl)-5-pivaloyloxyoxazole () proceeds via a hydrophobic binding step to give inactive pivaloyl thrombin, which slowly but fully reactivates under mildly alkaline conditions. Trypsin and chymotrypsin are also inactivated by . In contrast, plasmin is very slowly affected by high concentrations of that would inhibit thrombin almost instantaneously. These observations correlate with the selectivity of proflavin binding to these enzymes. The 2-methyl analog of shows poor binding to thrombin and consequently inactivates it much more slowly than does . 相似文献