排序方式: 共有60条查询结果,搜索用时 15 毫秒
41.
42.
Chromosomal DNA from 23 closely related, pathogenic strains of Escherichia
coli was digested and probed for the insertion sequences IS1, IS2, IS4,
IS5, and IS30. Under the assumption that elements residing in DNA
restriction fragments of the same apparent length are identical by descent,
parsimony analysis of these characters yielded a unique phylogenetic tree.
This analysis not only distinguished among bacterial strains that were
otherwise identical in their biochemical characteristics and enzyme
electrophoretic mobilities, but certain aspects of the topology of the tree
were consistent across several unrelated insertion elements. The
distribution of IS elements was then reexamined in light of the inferred
phylogenetic relationships to investigate the biological properties of the
elements, such as rates of insertion and deletion, and to discover apparent
recombinational events. The analysis shows that the pattern of distribution
of insertion elements in the bacterial genome is sufficiently stable for
epidemiological studies. Although the rate of recombination by conjugation
has been postulated to be low, at least two such events appear to have
taken place.
相似文献
43.
Homologues of glucosephosphate isomerase (GPI, EC 5.3.1.9) were purified to
homogeneity and kinetically characterized from Mytilus edulis and Isognomon
alatus, two bivalve molluscs experiencing contrasting thermal environments.
The enzyme isolated from I. alatus functions at warmer temperatures (25-35
C) than GPI from M. edulis, a species that inhabits colder marine littoral
habitats (5-20 C). The former exhibits apparent first-order (with respect
to substrate) catalytic rate constants (Vmax/KM) in vitro that become
progressively greater than the mussel enzyme as the assay temperature is
raised. Apparent zero-order catalytic rate constants (Vmax) are relatively
less differentiated. Catalytic efficiency, defined as the rate at which a
catalytic event occurs in either reaction direction for reference standard
states (substrate concentrations), is greater for the enzyme from the
tropical species (I. alatus) at all realistic combinations of temperature
and substrate concentration except for the lowest temperatures and highest
substrate concentrations, where the GPI from the boreal/temperate M. edulis
is more efficient. This pattern of catalytic divergence appears to be due
primarily to differentiation in Vmax/KM. These results and other published
data are reviewed and shown to be inconsistent with claims that adaptation
of enzymes to higher cell temperatures requires a loss in catalytic
efficiency.
相似文献
44.
45.
46.
This study focuses on the cytotoxic effects of fumonisin B1 (FB1) on both immortalised and immortalised and subsequently transfected normal human bronchial epithelial (NHBE) cells of human
origin using four bioassays. While the MTT, Neutral Red and hexosaminidase colorimetric assays showed little difference between
the toxic effects on the two related cell lines, the clonogenic assay, measuring cell survival and proliferation, indicated
that FB1 had a more toxic effect on the nontransfected cells. This kind ofin vitro approach using cells which retain many characteristics of normal cell growth and differentiation can go some way to developing
evaluation models for food safety in the case of mycotoxin contamination without resorting totally to whole animal testing.
Nevertheless, one or two cytotoxicity tests may be inadequate for a complete appraisal of toxic potential: rather, as wide
a range of methodologies as feasible should be employed initially before meaningful conclusions may be drawn. 相似文献
47.
M Kale R Ramsey-Goldman S Bernatsky MB Urowitz D Gladman PR Fortin M Petri E Yelin S Manzi S Edworthy O Nived S-C Bae D Isenberg A Rahman JG Hanly C Gordon S Jacobsen E Ginzler DJ Wallace GS Alarcón MA Dooley L Gottesman K Steinsson A Zoma J-L Senécal S Barr G Sturfelt L Dreyer L Criswell J Sibley JL Lee AE Clarke 《Arthritis research & therapy》2012,14(Z3):A15
48.
At the early onset of the 20th century, several studies already reported that the gray matter was implicated in the histopathology of multiple sclerosis
(MS). However, as white matter pathology long received predominant attention in this disease, and histological staining techniques
for detecting myelin in the gray matter were suboptimal, it was not until the beginning of the 21st century that the true extent and importance of gray matter pathology in MS was finally recognized. Gray matter damage was
shown to be frequent and extensive, and more pronounced in the progressive disease phases. Several studies subsequently demonstrated
that the histopathology of gray matter lesions differs from that of white matter lesions. Unfortunately, imaging of pathology
in gray matter structures proved to be difficult, especially when using conventional magnetic resonance imaging (MRI) techniques.
However, with the recent introduction of several more advanced MRI techniques, the detection of cortical and subcortical damage
in MS has considerably improved. This has important consequences for studying the clinical correlates of gray matter damage.
In this review, we provide an overview of what has been learned about imaging of gray matter damage in MS, and offer a brief
perspective with regards to future developments in this field. 相似文献
49.
50.
Sharon J. Marks Niall R. Moore Mo L. Clark Boyd JG Strauss T. Derek R. Hockaday 《Obesity (Silver Spring, Md.)》1996,4(1):1-7
Increased visceral adipose tissue is thought to contribute to impaired glucose tolerance. We studied 10 men with non-insulin dependent diabetes (NIDDM) before and after a 12-week intervention study using dexfenfluramine. Subjects had a mean body mass index (BMI) of 26.4 ± 1.7 kg\m2 and had an abdominal distribution of body fatness (waist-to hip ratio >0.9). Anthropometric indices, biochemistry, macronutrient intake from 7-day food records as well as a euglycaemic glucose clamp and magnetic resonance imaging (MRI) were performed at week 0 and week 12. Abdominal adipose tissue area measured by MRI was reduced from 854 ± 270 cm2 to 666 ± 231 cm2 (p=0.003) due mainly to a selective 32% reduction in visceral fat area from 484 ± 230 cm2 to 333 ± 72 cm2 (p=0.002). Insulin sensitivity improved from 0.29 ± 0.13 [min?1 (mU/L)] to 0.54 ± 0.21 [min?1 (mU/L)] (p=0.01) and C-peptide levels reduced from 0.77 ± 0.24 μmol/L to 0.58 ± 0.15 μmol/L (p=0.002). The reductions in fasting glucose and glycated haemoglobin failed to achieve significance. Fasting total cholesterol and triglyceride levels significantly reduced (p=<0.001 and p=0.021 respectively). There was a reduction in total energy intake (p=0.005) due to a significant reduction in calories obtained from fat (p<0.001). Thus dexfenfluramine was shown to be a useful adjunct therapy for the reduction of visceral fat in abdominally-obese men with NIDDM with an associated improvement in insulin sensitivity. 相似文献