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291.
Laser-Raman spectra of d-fructose in water at different concentrations were recorded, and assignments of the frequencies were proposed, based on earlier work on the Raman spectra of other sugars, and determination by other techniques of the composition of aqueous solutions of d-fructose as regards different isomers. It was found that the frequencies of vibration of the furanoid are higher than those of the pyranoid ring. The proportions of the furanoses and pyranoses, found from the ratio of the Raman intensities for the same modes of vibration, were similar to those found by other techniques. Shifts of intensities and frequencies were observed in the region of OH and CH bands, and were assigned to probable association between molecules of d-fructose and water. 相似文献
292.
Mohamed Mathlouthi Claudine Luu Anne Marie Meffroy-Biget Dang Vinh Luu 《Carbohydrate research》1980,81(2):213-223
The solute-solvent interactions of d-fructose, d-glucose, and sucrose in aqueous solution were studied by comparison of characteristic, Raman of the water and the sugar components. Shifts in frequency and intensity were observed in both the bending and the stretching regions of CH2 and H2O. The ratios of integrated, Raman intensities I(CH2)/I(H2O) of the CH2 peak and the H2O bending band, and I(CH)/I(OH) of the C-H stretching line to O-H stretching band were determined. Their evolutions in terms of mass-concentration display discontinuities at specific concentrations for each of the three sugars. These breaks were interpreted as changes in the hydrogen bonding of the various species. 相似文献
293.
Combining protein evolution and secondary structure 总被引:19,自引:9,他引:10
An evolutionary model that combines protein secondary structure and amino
acid replacement is introduced. It allows likelihood analysis of aligned
protein sequences and does not require the underlying secondary (or
tertiary) structures of these sequences to be known. One component of the
model describes the organization of secondary structure along a protein
sequence and another specifies the evolutionary process for each category
of secondary structure. A database of proteins with known secondary
structures is used to estimate model parameters representing these two
components. Phylogeny, the third component of the model, can be estimated
from the data set of interest. As an example, we employ our model to
analyze a set of sucrose synthase sequences. For the evolution of sucrose
synthase, a parametric bootstrap approach indicates that our model is
statistically preferable to one that ignores secondary structure.
相似文献
294.
Phylogenetic evidence for role-reversals of gender-associated mitochondrial DNA in Mytilus (Bivalvia: Mytilidae) 总被引:1,自引:0,他引:1
Hoeh WR; Stewart DT; Saavedra C; Sutherland BW; Zouros E 《Molecular biology and evolution》1997,14(9):959-967
Distinct gender-associated mitochondrial DNA (mtDNA) lineages (i.e.,
lineages which are transmitted either through males or through females)
have been demonstrated in two families of bivalves, the Mytilidae (marine
mussels) and the Unionidae (freshwater mussels), which have been separated
for more than 400 Myr. The mode of transmission of these M (for
male-transmitted) and F (for female-transmitted) molecules has been
referred to as doubly uniparental inheritance (DUI), in contrast to
standard maternal inheritance (SMI), which is the norm in animals. A
previous study suggested that at least three origins of DUI are required to
explain the phylogenetic pattern of M and F lineages in freshwater and
marine mussels. Here we present phylogenetic evidence based on partial
sequences of the cytochrome c oxidase subunit I gene and the 16S RNA gene
that indicates the DUI is a dynamic phenomenon. Specifically, we
demonstrate that F lineages in three species of Mytilus mussels, M. edulis,
M. trossulus, and M. californianus, have spawned separate lineages which
are now associated only with males. This process is referred to as
"masculinization" of F mtDNA. By extension, we propose that DUI may be a
primitive bivalve character and that periodic masculinization events
combined with extinction of previously existing M types effectively reset
the time of divergence between conspecific gender-associated mtDNA
lineages.
相似文献
295.
Charles F.B. Holmes Hue A. Luu France Carrier Francis J. Schmitz 《FEBS letters》1990,270(1-2):216-218
Acanthifolicin (9,10-epithio-okadaic acid from Pandoras acanthifolium) inhibited protein phosphatase-1 (PP1) similarly to okadaic acid (IC50 = 20 nM and 19 nM, respectively) but was slightly less active against protein phosphatase-2A (PP2A) (IC50 1 nM and 0.2 nM, respectively). Methyl esterification of acanthifolicin sharply reduced its activity. PP2A was inhibited with an IC50 = 5.0 μM, whilst PP1 was inhibited < 10% at 250 μM toxin. Okadaic acid methyl ester was similarly inactive whereas dinophysistoxin-1 (35-methyl okadaic acid) inhibited PP1/2A almost as potently as okadaic acid. Pure acanthifolicin/okadaic acid methyl ester may be useful as specific inhibitors of PP2A at 1–10 μM concentrations in vitro and perhaps in vivo. The data also indicate that a region on these toxins important for PP1/2A inhibition comprises the single carboxyl group. 相似文献
296.
Alexandre Kupferberg Gérard Cremel Patrick Behr Alain Van Dorsselaer Bang Luu Marcel Mersel 《Molecular and cellular biochemistry》1991,101(1):11-22
Summary The cytotoxicity of 7-hydroxycholesterol (7-OHC) was investigated on rat astrocyte primary cultures and spontaneously transformed cell lines derived from them. Confluent astrocyte primary cultures (normal cells) were unaffected by 20 µM 7(3-OHC over a period of 72 h whereas 30 µM markedly affected the viability of the transformed cells within the first 72 h. Both cell types incorporated 18% of the total amount of 7-OHC added to the cultures at concentrations of 20 µM or 30 µM. Cellular fractionation after incubation with 20 µM or 30 µM 7-OHC indicated that the plasma membrane incorporated 2 or 6 fold more 7-OHC than the intracellular one's respectively. Plasma membrane cholesterol (CH) and phospholipid (PL) analysis showed that 20 µM 7-OHC did not affect CH/PL in normal cells; in contrast, plasma membranes of transformed cells displayed a significant CH/PL decrease, which was more pronounced with 30 µM 7-OHC treatment. Fluorescence anisotropy measurements indicated that 20 µM 7-OHC slightly fluidified the plasma membrane of normal cells whereas it has not effect on that of the transformed cells one; however, an increase in plasma membrane fluidity was observed when the transformed cells were treated with 30 µM 7-OHC. Lactoperoxidase catalyzed radioiodination of cell surface proteins and subsequent autoradioelectrophoretic analysis demonstrated that the labelled protein pattern was unchanged when both cell types were incubated with 30 µM 7-OHC. 相似文献
297.
H Hietter B Luu F Goltzene D Zachary J Hoffmann A Van Dorsselaer 《European journal of biochemistry》1989,182(1):77-84
We have isolated two major 6-kDa peptides from extracts of corpora cardiaca of adult females of Locusta migratoria. These peptides have been characterized by peptide sequencing and liquid secondary-ion mass spectrometry. They are structurally related dimers, one (6278.5 Da) being a homodimer (A-A chains), the other (6280.5 Da) being a heterodimer (A-B chains). A 60% similarity exists between the A and B chains. Both peptides have been chemically synthesized and the synthetic compounds appeared to be identical to the native ones. Polyclonal antibodies raised against each of these peptides demonstrated that they were contained within the secretory granules of the intrinsic cells of the glandular lobes of the corpora cardiaca. The physiological significance of these two peptides is unknown but, using the synthetic peptides, we are currently probing their biological role. 相似文献
298.
Assignment of the human 3 beta-hydroxysteroid dehydrogenase gene (HSDB3) to the p13 band of chromosome 1 总被引:3,自引:0,他引:3
Three-beta-hydroxysteroid dehydrogenase (HSDB3) is the enzyme which catalyses the oxidative conversion of delta 5-3 beta-hydroxy steroids to the delta 4-3-keto configuration and is therefore involved in the biosynthesis of all classes of hormonal steroids, namely progesterone, glucocorticoids, mineralocorticoids, androgens, and estrogens. Deficiency of the enzyme is associated with congenital adrenal hyperplasia and is usually lethal in early life. Despite its crucial role, chromosome assignment of the gene for this enzyme has not been reported. Using in situ hybridization, we report that hybridization with labeled human HSDB3-specific cDNA yielded 27% of silver grains associated with chromosome 1 with a maximal concentration in the p13 band. 相似文献
299.
Edward C. Yeung Mark F. Belmonte Luu T. T. Tu Claudio Stasolla 《In vitro cellular & developmental biology. Plant》2005,41(5):584-590
Summary It is well known that glutathione is a ubiquitous and multifunctional compound which is important in maintaining cellular
redox homeostasis. The balance between the reduced (GSH) and oxidized (GSSG) forms of this tripeptide plays a fundamental
role in basic physiological and metabolic processes in plants. Recently, a remarkable amount of evidence has suggested that
the role of glutathione within the plant system extends beyond the basic metabolic functions and that it may ultimately act
as a modulator of plant development and morphogenesis. Therefore, it is not surpring that research has begung to focus on
using the glutathione redox pair system for improving regeneration of cultured cells. One of the major themes that has emerged
from in vitro studies is that GSH promotes cell proliferation, while GSSG promotes organized development. Thus, in vitro manipulation of this redox compound within the culture medium could lead to an enhancement of plant regeneration. 相似文献