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71.
Hilde De Boeck Frank G. Loontiens Halina Lis Nathan Sharon 《Archives of biochemistry and biophysics》1984,234(1):297-304
Erythrina cristagalli agglutinin, a dimeric lectin [J. L. Iglesias, et al. (1982) Eur. J. Biochem.123, 247–252] was shown by equilibrium dialysis to be bivalent for 4-methylumbelliferyl-β-d-galactoside. Upon binding to the lectin, this ligand showed a difference absorption spectrum with two maxima (at 322 and 336 nm) of equal intensity (Δ? = 1.2 × 103m?1 cm?1). A similar spectrum with a comparable value of Δ? was obtained with 4-methylumbelliferyl-N-acetyl-β-d-galactosaminide. Binding of methyl-α-d-galactoside, lactose, and N-acetyllactosamine all produced small but equally intense protein difference spectra with a maximum (Δ? = 2.8 × 102 M?1 cm?1) at 291.6 nm. Upon binding of N-dansyl-d-galactosamine to the lectin, there was a fivefold increase in fluorescence intensity of this ligand. The association constant for N-dansyl-d-galactosamine was caused by a very favorable ΔS° of the dansyl group without affecting the strictly carbohydrate-specific character of binding. N-Dansyl-d-galactosamine was employed as a fluorescent indicator ligand in substitution titrations. This involved the use of simple carbohydrates, N-acetyllactosamine, and oligosaccharides which occur in the carbohydrate units of N-glycoproteins; the latter were Gal(β → 4)GlcNAc(β1 → 2)Man, Gal(β1 → 4)GlcNAc(β1 → 6)Man, and Gal(β1 → 4)GlcNAc(β1 → 6)[Gal(β1 → 4)GlcNAc(β1 → 2)]Man. The titrations were performed at two temperatures to determine the thermodynamic parameters. In the series N-acetyl-d-galactosamine, methyl-α-d-galactoside, and lactose, ?ΔH° increased from 24 to 41 kJ mol?1; it increased further for N-acetyllactosamine and then remained unchanged for the N-acetyllactosamine-containing oligosaccharides (55 ± 1 kJ mol?1). This indicated that the site specifically accommodated the disaccharide structure with an important contribution of the 2-acetamido group in the penultimate sugar. Beyond this, no additional contacts seemed to be formed. This conclusion also followed from considerations of ΔS° values which became more unfavorable in the above series (?23 to ?101 ± 4 J mol?1 K?1); the most negative value of ΔS° was observed with N-acetyllactosamine and the three N-acetyllactosamine-containing oligosaccharides. 相似文献
72.
An analysis of previous spontaneous abortions and the frequencies of blood-group combinations in mother-child pairs was carried out in 500 gravidae. The rate of previous spontaneous abortions in blood-group-O women whose latest child has blood group B is significantly higher than in all other women. On the other hand, the combination mother B/child AB is rarer than expected, but no increase in the rate of previous spontaneous abortions is obvious among these women. These discrepancies are interpreted as an indication that prenatal selection associated with ABO incompatibility may operate at various stages from fertilization through pregnancy, and that different incompatible combinations may be subject to selection at different stages. 相似文献
73.
The association constants for the binding of various saccharides to hen egg-white lysozyme and human lysozyme have been measured by fluorescence titration. Among these are the oligosaccharides GlcNAc-beta(1 leads to 4)-MurNAc-beta(1 leads to 4)-GlcNAc-beta(1 leads to 4)-GlcNAc, GlcNAc-beta(1 leads to 4)-MurNAc-beta(1 leads to 4)-GlcNAc-beta(1 leads to 4)-N-acetyl-D-xylosamine, and GlcNAc-beta(1 leads to 4-GlcNAc-beta(1 leads to 4)-MurNAc, prepared here for the first time. The binding constants for saccharides which must have N-acetylmuramic acid, N-acetyl-D-glucosamine, or N-acetyl-D-xylosamine bound in subsite D indicate that there is no strain involved in the binding of N-acetyl-D-glycosamine in this site, and that the lactyl group of N-acetylmuramic acid (rather than the hydroxymethyl group) is responsible for the apparent strain previously reported for binding at this subsite. For hen egg-white lysozyme, the dependence of saccharide binding on pH or on a saturating concentration of Gd(III) suggests that the conformation of several of the complexes are different from one another and from that proposed for a productive complex. This is supported by fluorescence difference spectra of the various hen egg-white lysozyme-saccharide complexes. Human lysozyme binds most saccharides studied more weakly than the hen egg-white enzyme, but binds GlcNAc-beta(1 leads to 4)-MurNAc-beta(1leads to 4)-GlcNAc-beta(1 leads to 4)-MurNAc more strongly. It is suggested that subsite C of the human enzyme is "looser" than the equivalent site in the hen egg enzyme, so that the rearrangement of a saccharide in this subsite in response to introduction of an N-acetylmuramic acid residue into subsite D destabilizes the saccharide complexes of human lysozyme less than it does the corresponding hen egg-white lysozyme complexes. This difference and the differences in the fluorescence difference spectra of hen egg-white lysozyme and human lysozyme are ascribed mainly to the replacement of Trp-62 in hen egg-white lysozyme by Tyr-63 in the human enzyme. The implications of our findings for the assumption of superposition and additivity of energies of binding in individual subsites, and for the estimation of the role of strain in lysozyme catalysis, are discussed. 相似文献
74.
Tetrahymena pyriformis cells in the logarithmic phase of growth accumulate 2.5–3.75 times as much calcium per unit volume as is present in the growth medium. It appears that most of this calcium is stored in a non-ionic form, with approximately 30% existing in the cilia, near its site of action in effecting ciliary reversal. The exchange of extracellular 45Ca2+ with the major internal pools is extremely rapid, exhibiting a of less than 0.5 h. Sites located on the cilia are responsible for 35–50% of Ca2+ influx, with the remainder entering through other positions on the cell surface. 相似文献
75.
The heavy and light chains of pooled antibodies of the hybodont shark,Heterodontus francisci (horned shark), were subjected to amino acid sequence analysis. Yield determinations showed that more than 90% of the available polypeptides in the respective pools were sequenced. The heavy chains were homogeneous in the initial framework segment and showed a sequence homology of approximately 70% with the corresponding region of the more recently evolved nurse shark and a 45% homology with a human myeloma heavy chain. The light chains were less homogeneous and not identifiable as either kappa or lambda chains as known in higher species. The first half-cystine characteristics of the variable domain intrachain disulfide bridge of immunoglobulins was present in the same position (22 for heavy chains; 23 for light chains) in the horned shark as in mammalian species. The sequence analysis also suggested the presence of a hypervariable region in the horned shark light chains. The combined data imply that the antigen-binding function of immunoglobulins is mediated in much the same manner in this primitive shark as in more recently evolved species, including mammals. 相似文献
76.
Two types of pectoral girdles occur among frogs. Arciferal girdles have overlapping epicoracoid cartilages; in firmisternal girdles the epicoracoid cartilages are fused along the ventral midline. Cineradiographic experiments of jumping frogs show that the epicoracoid cartilages of arciferal girdles move relative to each other at the time of landing. Recordings of landings on a force platform reveal that the pectoral girdle of frogs is loaded compressively through the glenoid. This loading regime coupled with differential mobility between firmisternal and arciferal girdles results in differences in stress distribution in the two girdles during landing. The patterns of stress distribution suggest that variation seen among frogs in other aspects of pectoral morphology in addition to the condition of the epicoracoid cartilages may be best understood when analysed from a biomechanical perspective. 相似文献
77.
High-speed film analysis of the mechanism of take-off of a pigeon ascending nearly vertically reveals the pattern of movements of the wing segments and the bones within them during each of the five phases of the wingbeat cycle. Differences in the type and extent of wing movements between the upstroke and downstroke portions of the first and successive wingbeat cycles are explained with reference to the upward vertical jump made during the first wingbeat cycle. The presence during pigeon take-off of a non-steady state pattern of airfoil action similar to that seen in some insects at the beginning of the downstroke was verified. 相似文献
78.
Thidiazuron stimulates shoot organogenesis and somatic embryogenesis in white ash (Fraxinus americana L.) 总被引:3,自引:0,他引:3
Sharon Bates John E. Preece Nadia E. Navarrete J. W. Van Sambeek Gerald R. Gaffney 《Plant Cell, Tissue and Organ Culture》1992,31(1):21-29
Immature and mature nonstratified seeds of white ash (Fraxinus americana L.) were dissected transversely and 2/3 of each seed was placed onto agar-solidified Murashige and Skoog medium. Adventitious buds, shoots, and somatic embryos formed on callus, cotyledons, and hypocotyls of the resulting seedlings. Shoot organogenesis was induced on explants cultured on medium with 10 M thidiazuron but not on explants on media with benzyladenine (BA) or isopentenyladenine. Not all seed sources were equally capable of shoot organogenesis and embryogenesis. Atypical of adventitious regeneration of other woody plants, mature seed explants of white ash were more organogenic with shoots that elongated better than explants from immature seeds. Somatic embryogenesis was observed in cultures where mature seeds were first cultured for 4 weeks on a medium containing 10 M adenine 2,4-dichlorophenoxyacetic acid in combination with 0.1 and 1.0 M thidiazuron, followed by transfer to a medium containing 0.05 M 6-benzyladenine and 0.5 M naphthaleneacetic acid. Adventitious shoots and epicotyls from both seedlings and germinated somatic embryos were rooted under intermittent mist and acclimatized to the greenhouse.Abbreviations BA
6-benzyladenine
- 2,4-d
2,4-dichlorophenoxyacetic acid
- IBA
indolebutyric acid
- 2iP
isopentenyladenine
- NAA
naphthaleneacetic acid
- TDZ
thidiazuron-N-phenyl-N-1,2,3-thiadiazol-5-ylurea
- WPM
woody plant medium 相似文献
79.
Commercially available crystalline native and recombinant firefly luciferases were compared. The two types of luciferase had indistinguishable responses to variation in ATP and luciferin concentrations and to omission of reaction components. The time courses of light production, the responses to nucleotide analogues, and the stability of the enzymes under several storage conditions were identical. The native enzyme had a slightly greater specific activity and was more sensitive to trypsin degradation. These differeces are probably attributable to differences in conformation. 相似文献
80.
We report the production of a monoclonal antibody (MAb 526) that recognizes a novel, developmentally regulated nuclear protein expressed in neurons throughout the rat nervous system. Analysis of whole brain and cell nuclear extracts by SDS-PAGE and immunoblotting determined that MAb 526 recognizes a single nuclear protein (np) of apparent molecular weight 42 kD, designated np526, as well as a slightly larger (ca. 44 kD) cytoplasmic protein. Light microscopic immunocytochemistry showed np526 to be present in neurons of all types throughout the central and peripheral nervous systems. Nuclei of both fibrous and protoplasmic astrocytes were also immunoreactive, but oligodendrocyte nuclei were negative. Positive, but highly variable immunocytochemical staining of nonneural cell nuclei in a variety of other tissues was also observed. Electron microscopic (EM) immunocytochemistry using pre-embedding peroxidase methods revealed that np526 is associated with euchromatin or with the edges of condensed chromatin bundles in neurons, indicating that it is likely to be a chromosomal protein. Most interestingly, the expression of np526 was found to be developmentally regulated in brain. Immunocytochemical analysis of the developing cerebral cortex from embryonic day (E) 16 to postnatal day (P) 4 and cerebellum from P4 to P18 revealed that np526 first appears in central neurons following the cessation of mitosis and that the intensity of nuclear staining increases during subsequent neuronal maturation. To our knowledge, np526 is the first presumptive chromosomal protein whose expression has been precisely correlated with the early postmitotic differentiation of mammalian neurons. 相似文献