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1.
2.
Separation of large DNA restriction fragments on a size-exclusion column by a nonideal mechanism 总被引:1,自引:0,他引:1
Double-strand DNA (dsDNA) restriction fragments were chromatographed on the DuPont Bioseries GF-250 column. Two anomolous chromatographic properties were observed. (1) A triphasic dependence of retention on dsDNA chain length was observed. Small DNA fragments (less than 500 base pairs) displayed typical size exclusion, intermediate size DNA (800-5000 base pairs) eluted in the void volume, and larger DNA fragments were increasingly retained. (2) The void volume for nucleic acids was less than that for large polypeptides. The retention of moderately large DNA fragments increased linearly as the square root of the chain length over the range 5.5 to 50 kilobase pairs (ca. 3-30 X 10(6) Mr). A number of eluant manipulations were carried out in order to examine the mechanism by which the larger DNA fragments were being retained and separated. Evidence was not obtained to support either ion exchange or reverse phase as the retention mechanism. The usefulness of such a column for molecular biological manipulations is illustrated by the rapid isolation of homogeneous viral DNA fragments resected from their cloning vectors with restriction endonucleases. 相似文献
3.
Determination of plasma [18F]-6-fluorodopa during positron emission tomography: elimination and metabolism in carbidopa treated subjects 总被引:1,自引:0,他引:1
An investigation of the metabolism of [18F]-6-fluorodopa (FDOPA) given to carbidopa treated subjects for scanning by positron emission tomography (PET) has been carried out by analysis of plasma. Reverse phase ion pair HPLC and alumina extraction were employed to fractionate and identify the [18F]-labelled compounds of plasma over a two hour period. During this time, the plasma levels of both total 18F and FDOPA decreased as a bi-exponential function of time. The rates of 18F, but not FDOPA, elimination were observed to decrease with age. In addition to FDOPA, only one other major peak of radioactivity was resolved by HPLC. Identification of this compound as the O-methylated derivative of FDOPA (MeFDOPA) is based on its shared HPLC elution time with in vitro synthesized O-[methyl-14C]-FDOPA. The ratio of the concentration of MeFDOPA to FDOPA (MeFDOPA/FDOPA) in plasma increased linearly with time, and the slope of this linear relationship decreased with the age of the individual. 相似文献
4.
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
5.
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
6.
The 12th J. A. F. Stevenson memorial lecture. Aging, Alzheimer's disease, and the cholinergic system
P L McGeer 《Canadian journal of physiology and pharmacology》1984,62(7):741-754
Aging does not affect tissues in a uniform fashion. Within the brain, substantial neuronal dropout occurs with age in the cholinergic medial basal forebrain complex, the noradrenergic locus coeruleus, and the dopaminergic substantia nigra pars compacta. These areas are also struck by diseases that are sharply age dependent. Alzheimer's disease causes neuronal destruction in the cholinergic cells of the medial basal forebrain and noradrenergic cells of the locus coeruleus. Parkinson's disease causes neuronal destruction mainly in the substantia nigra but with some destruction in the locus coeruleus. Parkinsonism-dementia affects all three areas. Alzheimer's disease is responsible for 50-60% of all cases of dementia. Severe dementia rises in frequency from less than 1% of the population at age 65-70 to over 15% by age 85. The cause of the disease is unknown. No method of prevention is known and present treatments are ineffective, although modest improvement has been reported for various therapeutic regimens designed to stimulate the cholinergic system. The neuronal systems identified as being affected in Alzheimer's disease and in the dementia of Parkinsonism correspond with those shown many years ago to be associated with the reticular activating system. This correspondence permits a new hypothesis of cognition and memory to be put forward, as well as a reinterpretation of data from animal research on the reticular activating system performed over a quarter of a century ago. The locus coeruleus is proposed as the noradrenergic element sensitizing the cortex to conscious recognition of real time events. The medial basal forebrain complex is proposed as the system registering the conscious event for storage and as the readout device when it is subsequently redisplayed in the cortex as memory. Storage could either be in the temporal lobe, in several areas of cortex with feedback to the medial basal forebrain, or in the cholinergic cells themselves. 相似文献
7.
Injection of folic acid (FA) into the nucleus substantia innominata (NSI) was found to decrease [3H]quinuclidinyl benzilate ([3H]QNB) binding in the frontal cortex, pyriform cortex, amygdala, and the NSI itself without changing the KD. Binding in the thalamus, caudate nucleus, hippocampus, and substantia nigra was not affected. [3H]Flunitrazepam binding was unchanged in all eight regions studied. Previous work indicates FA injections into the NSI produce epileptiform activity and cause loss of GABAergic and possibly other neurons in the frontal and pyriform cortices, the amygdala, and thalamus. The reductions of [3H]QNB binding in the first three of these regions are interpreted as indicating that many of the neurons lost are cholinoceptive, a finding that supports the previous hypothesis that activation of cholinergic projections from the NSI is an important part of the mechanism of cell loss in these regions. 相似文献
8.
Distribution of tyrosine hydroxylase in human and animal brain 总被引:11,自引:5,他引:6
The activity of tyrosine hydroxylase (EC 1.10.3.1) when assayed under ideal conditions in young human brains, was comparable to that in brains of other species in level of activity and distribution. The highest levels of activity were in the putamen, caudate nucleus and substantia nigra, in keeping with data on other species. The caudate activity in human brain appeared to decrease substantially with increasing age. In both humans and baboons, the enzyme in the neostriatum was particle-bound and inhibited by the 2-amino-4-hydroxy-6,7-dimethyltetrahydropteridine cofactor system. In the substantia nigra it was soluble and stimulated by the 2-amino-4-hydroxy-6,7-dimethyltetrahydropteridine cofactor system. The data suggest that tyrosine hydroxylase may be produced in a soluble form in the cell bodies of the substantia nigra but become bound as it moves toward the nerve endings in the putamen and caudate nucleus. The bound form of the enzyme was unstable but the soluble form exhibited considerable stability. 相似文献
9.
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
10.