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排序方式: 共有177条查询结果,搜索用时 15 毫秒
1.
2.
P K Wong J L Poyer C M DuBose R A Floyd 《The Journal of biological chemistry》1988,263(23):11296-11301
The addition of hydralazine (1-hydrazinophthalazine) to rat liver mitochondria metabolizing malate/glutamate causes formation of a carbon-centered free radical which was spin-trapped with phenyl-t-butylnitrone (PBN) or dimethylpyrrolidine-N-oxide (DMPO). The coupling constants of the spin-trapped free radical were AN = 16.1, AH beta = 4.6 G for PBN and AN = 15.9, AH beta = 18.9 G for DMPO-trapped radical in aqueous solution. The spin-trapped free radical was shown to be the carbon dioxide anion free radical by independent synthesis, high pressure liquid chromatography separation, and electron paramagnetic resonance characterization. The amount of carbon dioxide anion free radical produced was absolutely dependent upon the presence of hydralazine and varied depending on mitochondrial substrate, with by far the highest amount produced by pyruvate. Studies with 13C-labeled pyruvate demonstrated that the carbon dioxide free radical came from C-1 of this compound. 相似文献
3.
A comparative description of mitochondrial DNA differentiation in selected avian and other vertebrate genera 总被引:14,自引:1,他引:13
Levels of mitochondrial DNA (mtDNA) sequence divergence between species
within each of several avian (Anas, Aythya, Dendroica, Melospiza, and
Zonotrichia) and nonavian (Lepomis and Hyla) vertebrate genera were
compared. An analysis of digestion profiles generated by 13-18 restriction
endonucleases indicates little overlap in magnitude of mtDNA divergence for
the avian versus nonavian taxa examined. In 55 interspecific comparisons
among the avian congeners, the fraction of identical fragment lengths (F)
ranged from 0.26 to 0.96 (F = 0.46), and, given certain assumptions, these
translate into estimates of nucleotide sequence divergence (p) ranging from
0.007 to 0.088; in 46 comparisons among the fish and amphibian congeners, F
values ranged from 0.00 to 0.36 (F = 0.09), yielding estimates of P greater
than 0.070. The small mtDNA distances among avian congeners are associated
with protein-electrophoretic distances (D values) less than approximately
0.2, while the mtDNA distances among assayed fish and amphibian congeners
are associated with D values usually greater than 0.4. Since the
conservative pattern of protein differentiation previously reported for
many avian versus nonavian taxa now appears to be paralleled by a
conservative pattern of mtDNA divergence, it seems increasingly likely that
many avian species have shared more recent common ancestors than have their
nonavian taxonomic counterparts. However, estimates of avian divergence
times derived from mtDNA- and protein-calibrated clocks cannot readily be
reconciled with some published dates based on limited fossil remains. If
the earlier paleontological interpretations are valid, then protein and
mtDNA evolution must be somewhat decelerated in birds. The empirical and
conceptual issues raised by these findings are highly analogous to those in
the long-standing debate about rates of molecular evolution and times of
separation of ancestral hominids from African apes.
相似文献
4.
Methods for computing the standard errors of branching points in an evolutionary tree and their application to molecular data from humans and apes 总被引:23,自引:2,他引:21
Statistical methods for computing the standard errors of the branching
points of an evolutionary tree are developed. These methods are for the
unweighted pair-group method-determined (UPGMA) trees reconstructed from
molecular data such as amino acid sequences, nucleotide sequences,
restriction-sites data, and electrophoretic distances. They were applied to
data for the human, chimpanzee, gorilla, orangutan, and gibbon species.
Among the four different sets of data used, DNA sequences for an
895-nucleotide segment of mitochondrial DNA (Brown et al. 1982) gave the
most reliable tree, whereas electrophoretic data (Bruce and Ayala 1979)
gave the least reliable one. The DNA sequence data suggested that the
chimpanzee is the closest and that the gorilla is the next closest to the
human species. The orangutan and gibbon are more distantly related to man
than is the gorilla. This topology of the tree is in agreement with that
for the tree obtained from chromosomal studies and DNA-hybridization
experiments. However, the difference between the branching point for the
human and the chimpanzee species and that for the gorilla species and the
human-chimpanzee group is not statistically significant. In addition to
this analysis, various factors that affect the accuracy of an estimated
tree are discussed.
相似文献
5.
Oxygen- and carbon-centered free radical formation during carbon tetrachloride metabolism. Observation of lipid radicals in vivo and in vitro 总被引:5,自引:0,他引:5
P B McCay E K Lai J L Poyer C M DuBose E G Janzen 《The Journal of biological chemistry》1984,259(4):2135-2143
Free radical reactions involved in the metabolism of carbon tetrachloride by rat liver have been considered to be a cause of at least part of the injury resulting from exposure to this halocarbon. In an earlier study employing electron spin resonance and spin-trapping techniques, we demonstrated that trichloromethyl (13.CCl3) radicals are readily observed in rat liver microsomes metabolizing 13CCl4, and that the same radical could be shown to form in vivo in the liver of intact rats given a single dose of 13CCl4. This report describes the production of lipid dienyl (L.) and oxygen-centered lipid radicals (LO. or LOO., or both) in in vitro systems metabolizing 13CCl4, and also the formation of lipid dienyl radicals (L.) in liver of intact animals exposed to CCl4. The radicals appear to be produced in a sequence of reactions governed among other things by the oxygen tension in the system. The lipid radicals (L.) which form in intact liver of CCl4-treated rats are apparently the result of an attack on lipids of the endoplasmic reticulum by 13.CCl3 radicals formed by reductive cleavage to CCl4 and are the initial intermediates in the process of lipid peroxidation. These investigations demonstrate that while the events occurring in liver microsomes in vitro appear to parallel those which take place in intact liver in vivo, the conditions in vivo make the spin-trapping studies of radicals in intact animals much more selective than it is in vitro for a given spin trap, and requires the use of more than one type of spin-trapping agent to detect different radical species in vivo. 相似文献
6.
We used whole-cell patch-clamp recording techniques to investigate G protein-activated currents in cultured rat retinal pigment
epithelial (RPE) cells. Using 140 mm KCl intracellular and 130 mm NaCl extracellular solutions, rat RPE cells possessed both inward and outward K+ currents. Upon addition of the nonhydrolyzable guanine triphosphate analogue, guanosine-5′-O-(3-thiophosphate) (GTPγS, 0.1
mm), to the recording electrode, a nonspecific cation (NSC) current was elicited. The NSC current had a mean reversal potential
of +5.7 mV in 130 mm extracellular NaCl with Cs+-aspartate in the pipette, and was not affected by alterations in the extracellular Ca2+ or Cl− concentration. The GTPγS-activated current was found to be permeable to several monovalent cations (K+, Na+, choline, TRIS, and NMDG). Addition of fluoroaluminate, an activator of large molecular weight heterotrimeric GTP-binding
proteins (G proteins), to the intracellular recording solution activated the NSC current. The G protein involved was pertussis
toxin (PTX)-sensitive, since GTPγS failed to activate the NSC current in cells pretreated with PTX. Further investigation
of second messenger molecules suggested that activation of the NSC current was not affected by alterations in intracellular
Ca2+ or ATP. From these results, we conclude that a G protein-regulated NSC current is present in rat RPE cells. Activation of
the NSC current may sufficiently depolarize RPE cells to activate outward K+ currents. This would provide a mechanism by which these cells could rid themselves of accumulated K+.
Received: 25 January 1996/Revised: 24 April 1996 相似文献
7.
Anonymous nuclear DNA markers in the American oyster and their implications for the heterozygote deficiency phenomenon in marine bivalves 总被引:4,自引:0,他引:4
A puzzling population-genetic phenomenon widely reported in allozyme
surveys of marine bivalves is the occurrence of heterozygote deficits
relative to Hardy-Weinberg expectations. Possible explanations for this
pattern are categorized with respect to whether the effects should be
confined to protein-level assays or are genomically pervasive and expected
to be registered in both protein- and DNA-level assays. Anonymous nuclear
DNA markers from the American oyster were employed to reexamine the
phenomenon. In assays based on the polymerase chain reaction (PCR), two
DNA-level processes were encountered that can lead to artifactual genotypic
scorings: (a) differential amplification of alleles at a target locus and
(b) amplification from multiple paralogous loci. We describe symptoms of
these complications and prescribe methods that should generally help to
ameliorate them. When artifactual scorings at two anonymous DNA loci in the
American oyster were corrected, Hardy-Weinberg deviations registered in
preliminary population assays decreased to nonsignificant values.
Implications of these findings for the heterozygote-deficit phenomenon in
marine bivalves, and for the general development and use of PCR-based
assays, are discussed.
相似文献
8.
9.
10.
The accessibility of embryonic and adult neurons within invertebrate nervous systems has made them excellent subjects for
neurobiological study. The ability to readily identify individual neurons, together with their great capacity for regeneration,
has been especially beneficial to investigations of synapse formation and the specificity of neuronal connectivity. Many invertebrate
neurons survive for long periods following isolation into primary cell culture. In addition, they readily extend new neuritic
arbors and form electrical and chemical connections at sites of contact. Thus, cell culture approaches have allowed neuroscientists
greater access to, and resolution of, events underlying neurite outgrowth and synaptogenesis. Studies of identified neuromuscular
synapses ofHelisoma have determined a number of signaling mechanisms involved in transsynaptic communication at sites of neuron-target contact.
At these sites, both anterograde and retrograde signals regulate the transformation of growth cones into functional presynaptic
terminals. We have found that specific muscle targets induce both global and local changes in neurotransmitter secretion and
intracellular calcium handling. Here we review recent studies of culturedHelisoma synapses and discuss the mechanisms thought to govern chemical synapse formation in these identified neurons and those of
other invertebrate species. 相似文献