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111.
112.
We have studied the interaction of coenzyme Q with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its metabolites, 1-methyl-4-phenyl-2,3-dihydropyridinium (MPDP(+)) and 1-methyl-4-phenylpyridinium (MPP(+)), the real neurotoxin to cause Parkinson's disease. Incubation of MPTP or MPDP(+) with rat brain synaptosomes induced complete reduction of endogenous ubiquinone-9 and ubiquinone-10 to corresponding ubiquinols. The reduction occurred in a time- and MPTP/MPDP(+) concentration-dependent manner. The reduction of ubiquinone induced by MPDP(+) went much faster than that by MPTP. MPTP did not reduce liposome-trapped ubiquinone-10, but MPDP(+) did. The real toxin MPP(+) did not reduce ubiquinone in either of the systems. The reduction by MPTP but not MPDP(+) was completely prevented by pargyline, a type B monoamine oxidase (MAO-B) inhibitor, in the synaptosomes. The results indicate that involvement of MAO-B is critical for the reduction of ubiquinone by MPTP but that MPDP(+) is a reductant of ubiquinone per se. It is suggested that ubiquinone could be an electron acceptor from MPDP(+) and promote the conversion from MPDP(+) to MPP(+) in vivo, thus accelerating the neurotoxicity of MPTP. 相似文献
113.
Introns are generally believed to evolve too rapidly and too erratically to be of much use in phylogenetic reconstructions.
Few phylogenetically informative intron sequences are available, however, to ascertain the validity of this supposition. In
the present study the supposition was tested on the example of the mammalian class II major histocompatibility complex (Mhc) genes of the DRB family. Since the Mhc genes evolve under balancing selection and are believed to recombine or rearrange frequently, the evolution of their introns
could be expected to be particularly rapid and subject to scrambling. Sequences of intron 4 and 5 DRB genes were obtained from polymerase chain reaction-amplified fragments of genomic DNA from representatives of six eutherian
orders—Primates, Scandentia, Chiroptera, Dermoptera, Lagomorpha, and Insectivora. Although short stretches of the introns
have indeed proved to be unalignable, the bulk of the intron sequences from all six orders, spanning >85 million years (my)
of evolution, could be aligned and used in a study of the tempo and mode of intron evolution. The analysis has revealed the
Mhc introns to evolve at a rate similar to that of other genes and of synonymous sites of non-Mhc genes. No evidence of homogenization or large-scale scrambling of the intron sequences could be found. The Mhc introns apparently evolve largely by point mutations and insertions/deletions. The phylogenetic signals contained in the
intron sequences could be used to identify Scandentia as the sister group of Primates, to support the existence of the Archonta
superorder, and to confirm the monophyly of the Chiroptera.
Received: 26 October 1998 / Accepted: 21 December 1998 相似文献
114.
Cytoplasmic dynein is a minus-end directed microtubule motor and plays important roles in the transport of various intracellular cargoes. Cytoplasmic dynein comprises two identical heavy chains and forms a dimer (double-headed dynein); the total molecular weight of the cytoplasmic dynein complex is about 1.5 million. The dynein motor domain is structurally very different from those of kinesin and myosin, and our understanding of the mechanisms of dynein energy transduction is limited mainly because of the difficulty in obtaining a sufficient quantity of purified and active cytoplasmic dynein. We purified cytoplasmic dynein, which was free from dynactin and other dynein-associated proteins. The purified cytoplasmic dynein was active in an in vitro motility assay. The controlled dialysis of the purified dynein against 4 M urea resulted in its complete dissociation into monomeric species (single-headed dynein). The separation of the dynein heads by the treatment was reversible. The MgATPase activities of the single-headed and reconstituted double-headed dynein were comparable to that of intact dynein. The double-headed dynein bundled microtubules in the absence of ATP; the single-headed dynein did not. The single-headed dynein produced in vitro microtubule-gliding motility at velocities very similar to those of double-headed dynein at various ATP concentrations. These results indicate that a single cytoplasmic dynein heavy chain is sufficient to produce robust microtubule motility. Application of the double- and single-headed dynein molecules in various assay systems will elucidate the mechanism of action of the cytoplasmic dynein. 相似文献
115.
Toba S Gibson TM Shiroguchi K Toyoshima YY Asai DJ 《Cell motility and the cytoskeleton》2004,58(1):30-38
An important challenge is to understand the functional specialization of dynein heavy chains. The ciliary outer arm dynein from Tetrahymena thermophila is a heterotrimer of three heavy chains, called alpha, beta and gamma. In order to dissect the contributions of the individual heavy chains, we used controlled urea treatment to dissociate Tetrahymena outer arm dynein into a 19S beta/gamma dimer and a 14S alpha heavy chain. The three heavy chains remained full-length and retained MgATPase activity. The beta/gamma dimer bound microtubules in an ATP-sensitive fashion. The isolated alpha heavy chain also bound microtubules, but this binding was not reversed by ATP. The 19S beta/gamma dimer and the 14S alpha heavy chain could be reconstituted into 22S dynein. The intact 22S dynein, the 19S beta/gamma dimer, and the reconstituted dynein all produced microtubule gliding motility. In contrast, the separated alpha heavy chain did not produce movement under a variety of conditions. The intact 22S dynein produced movement that was discontinuous and slower than the movement produced by the 19S dimer. We conclude that the three heavy chains of Tetrahymena outer arm dynein are functionally specialized. The alpha heavy chain may be responsible for the structural binding of dynein to the outer doublet A-tubule and/or the positioning of the beta/gamma motor domains near the surface of the microtubule track. 相似文献
116.
Hayakawa F Ishizu Y Hoshino N Yamaji A Ando T Kimura T 《Bioscience, biotechnology, and biochemistry》2004,68(9):1825-1830
The ability of various tea catechins to generate H2O2 and the hydroxyl radical in the presence of the Cu2+ ion was investigated and compared with the effect of iron ions. The presence of Cu2+ accelerated the generation of H2O2 by EGC, while EGCg with Cu2+ generated a little H2O2. The presence of iron ions inhibited the generation of H2O2 by EGC. EGC and EC with Cu2+ generated the hydroxyl radical, while EGCg and ECg with Cu2+ did not. The fact that EGCg showed less prooxidative activity than EGC can be explained by the chelating ability of catechin gallates to metal ions under the experimental conditions. 相似文献
117.
Gaku?KUDOEmail author Yoko?NISHIKAWA Tetsuya?KASAGI Shoji?KOSUGE 《Ecological Research》2004,19(2):255-259
To predict the effect of global warming on plant reproductive success, seed-sets of spring ephemerals were compared between a year of extremely warm spring (2002) and normal years at cool-temperate deciduous forests in northern Japan. The spring of 2002 was the warmest in the last 40years and most spring-ephemeral plants bloomed 7–17days earlier than usual. The seed-set of bumblebee-pollinated Corydalis ambigua drastically decreased in 2002 in every population. The small bee-pollinated Gagea lutea also significantly decreased in 2002. However, the seed-sets of two fly pollinated species, Adonis ramosa and Anemone flaccida, were not influenced by early flowering. These results indicat that the effect of global warming on seed production of spring ephemerals differs between species depending on the type of pollinators, and that bee-pollinated species can have serious impacts on reproductive success as a result of climate change. 相似文献
118.
Saito Y Shiga A Yoshida Y Furuhashi T Fujita Y Niki E 《Bioscience, biotechnology, and biochemistry》2004,68(4):781-786
Rosemary is commonly used as a spice and a flavoring agent in food processing. Although the antioxidative properties of its extracts have been investigated, there have been few reports on the volatile components of rosemary. We designed a novel antioxidative system which can generate the volatile constituents in the gaseous phase from a rosemary extract and evaluated the gaseous antioxidative activities against both lipid peroxidation and cell death induced by nitrogen dioxide and ultraviolet radiation. The antioxidative effects of the major volatile components on the oxidation of linoleic acid induced by azo compounds were also investigated in a solution. The volatile components in the novel antioxidative system suppressed the Jurkat cell death induced by nitrogen dioxide and the intracellular formation of reactive oxygen species in fibroblast cells induced by ultraviolet radiation. 1,8-Cineole among the volatile components exerted an antioxidative effect against the oxidation of linoleic acid in a solution induced by azo compounds and ultraviolet radiation. These data suggest that the volatile constituents of a rosemary extract had antioxidative properties and that gaseous exposure antioxidant is a promising method for promoting health. 相似文献
119.
Murakami Y Pasqualetti M Takio Y Hirano S Rijli FM Kuratani S 《Development (Cambridge, England)》2004,131(5):983-995
During development, the vertebrate hindbrain is subdivided along its anteroposterior axis into a series of segmental bulges called rhombomeres. These segments in turn generate a repeated pattern of rhombomere-specific neurons, including reticular and branchiomotor neurons. In amphioxus (Cephalochordata), the sister group of the vertebrates, a bona fide segmented hindbrain is lacking, although the embryonic brain vesicle shows molecular anteroposterior regionalization. Therefore, evaluation of the segmental patterning of the central nervous system of agnathan embryos is relevant to our understanding of the origin of the developmental plan of the vertebrate hindbrain. To investigate the neuronal organization of the hindbrain of the Japanese lamprey, Lethenteron japonicum, we retrogradely labeled the reticulospinal and branchial motoneurons. By combining this analysis with a study of the expression patterns of genes identifying specific rhombomeric territories such as LjKrox20, LjPax6, LjEphC and LjHox3, we found that the reticular neurons in the lamprey hindbrain, including isthmic, bulbar and Mauthner cells, develop in conserved rhombomere-specific positions, similar to those in the zebrafish. By contrast, lamprey trigeminal and facial motor nuclei are not in register with rhombomere boundaries, unlike those of gnathostomes. The trigeminal-facial boundary corresponds to the rostral border of LjHox3 expression in the middle of rhombomere 4. Exogenous application of retinoic acid (RA) induced a rostral shift of both the LjHox3 expression domain and branchiomotor nuclei with no obvious repatterning of rhombomeric segmentation and reticular neurons. Therefore, whereas subtype variations of motoneuron identity along the anteroposterior axis may rely on Hox-dependent positional values, as in gnathostomes, such variations in the lamprey are not constrained by hindbrain segmentation. We hypothesize that the registering of hindbrain segmentation and neuronal patterning may have been acquired through successive and independent stepwise patterning changes during evolution. 相似文献
120.
Ide T Takahashi Y Kushiro M Tachibana M Matsushima Y 《The Journal of nutritional biochemistry》2004,15(3):169-178
N-3 fatty acids exert a potent serum lipid-lowering effect in rodents mainly by affecting hepatic fatty acid oxidation and synthesis. However, it has been observed that fish oil and docosahexaenoic acid ethyl ester do not lower serum lipid levels in apolipoprotein E (apoE)-knockout (Apoetm1Unc) mice generated by gene targeting. To test the hypothesis that apoE expression is required for n-3 fatty acid-dependent regulation of serum lipid levels and hepatic fatty acid metabolism, we examined the effect of fish oil and n-3 fatty acid ethyl esters on the activity and gene expression of hepatic enzymes involved in fatty acid oxidation and synthesis using an alternative apoE-deficient mouse model with the BALB/c genetic background (BALB/c.KOR-Apoeshl). ApoE-deficient mice were fed diets containing 9.4% palm oil, fish oil, or 5.4% palm oil and 1% EPA plus 3% DHA ethyl esters for 15 days. In contrast to the reported data on apoE-knockout mice, fish oil and n-3 fatty acid ethyl esters greatly decreased serum triacylglycerol, cholesterol, and phospholipid levels in the Apoeshl mice. The decreases were greater with fish oil than with ethyl esters. The alterations by dietary n-3 fatty acids of serum lipid levels were accompanied by parallel changes in the activity and mRNA levels of enzymes involved in hepatic fatty acid oxidation and synthesis. The reason for the discrepancy between the results of the current study and previous studies is unknown. However, our study at least indicates that a lack of apoE expression does not necessarily accompany deficits in the n-3 fatty acid-dependent regulation of serum lipid levels and hepatic fatty acid metabolism. 相似文献