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Expression of the Escherichia coli Catabolic Threonine Dehydratase in Corynebacterium glutamicum and Its Effect on Isoleucine Production 下载免费PDF全文
S. Guillouet A. A. Rodal G.-H. An P. A. Lessard A. J. Sinskey 《Applied microbiology》1999,65(7):3100-3107
The catabolic or biodegradative threonine dehydratase (E.C. 4.2.1.16) of Escherichia coli is an isoleucine feedback-resistant enzyme that catalyzes the degradation of threonine to α-ketobutyrate, the first reaction of the isoleucine pathway. We cloned and expressed this enzyme in Corynebacterium glutamicum. We found that while the native threonine dehydratase of C. glutamicum was totally inhibited by 15 mM isoleucine, the heterologous catabolic threonine dehydratase expressed in the same strain was much less sensitive to isoleucine; i.e., it retained 60% of its original activity even in the presence of 200 mM isoleucine. To determine whether expressing the catabolic threonine dehydratase (encoded by the tdcB gene) provided any benefit for isoleucine production compared to the native enzyme (encoded by the ilvA gene), fermentations were performed with the wild-type strain, an ilvA-overexpressing strain, and a tdcB-expressing strain. By expressing the heterologous catabolic threonine dehydratase in C. glutamicum, we were able to increase the production of isoleucine 50-fold, whereas overexpression of the native threonine dehydratase resulted in only a fourfold increase in isoleucine production. Carbon balance data showed that when just one enzyme, the catabolic threonine dehydratase, was overexpressed, 70% of the carbon available for the lysine pathway was redirected into the isoleucine pathway. 相似文献
155.
Eric P. Bergquam Nancy Avery Stanley M. Shiigi Michael K. Axthelm Scott W. Wong 《Journal of virology》1999,73(9):7874-7876
Recent DNA sequence analysis indicates that rhesus rhadinovirus (RRV) is a member of the lymphotropic gamma-2 herpesvirus family. To determine if RRV is lymphotropic, peripheral blood mononuclear cells from naturally infected monkeys were separated by immunomagnetic bead depletion and analyzed for the presence of RRV by virus isolation and nested PCR. The recovery and consistent detection of RRV in the CD20(+)-enriched fraction clearly demonstrates that B lymphocytes are a major site of virus persistence. 相似文献
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The invasive freshwater snail Tarebia granifera (Lamarck, 1822) was first reported in South Africa in 1999 and it has become widespread across the country, with some evidence to suggest that it reduces benthic macroinvertebrate biodiversity. The current study aimed to identify the primary abiotic drivers behind abundance patterns of T. granifera, by comparing the current abundance of the snail in three different regions, and at three depths, of the highly modified Nseleni River in KwaZulu-Natal, South Africa. Tarebia granifera was well established throughout the Nseleni River system, with an overall preference for shallow waters and seasonal temporal patterns of abundance. Although it is uncertain what the ecological impacts of the snail in this system are, its high abundances suggest that it should be controlled where possible and prevented from invading other systems in the region. 相似文献
158.
Ratamess NA Faigenbaum AD Hoffman JR Kang J 《Journal of strength and conditioning research / National Strength & Conditioning Association》2008,22(1):103-111
The purpose of the present investigation was to examine the influence of resistance training with a personal trainer versus unsupervised resistance training on the self-selected intensities used by women during resistance exercise. Forty-six resistance-trained women (age = 26.6 +/- 6.4 years; body mass = 64.2 +/- 10.9 kg) who either trained individually (n = 27; No PT) or with a personal trainer (n = 19; PT) were carefully instructed to select a weight they used in their own resistance training workouts that enabled the completion of 10 repetitions for the chest press (CP), leg press (LP), seated row (SR), and leg extension (LE) exercises. Each participant was subsequently tested for one repetition-maximum (1RM) strength on each exercise, and the self-selected intensity was calculated based on a percent of each 1RM value. For self-selected relative intensity, the PT group selected significantly greater intensities for LP (50% vs. 41%), CP (57.4% vs. 48%), and SR (56% vs. 42%) whereas a trend (p = 0.10) was observed for LE (43% vs. 38%) compared with No PT. Overall, the average self-selected intensity for all exercises was approximately 51.4% in PT group and approximately 42.3% in the No PT group. 1RM values for LP, LE, and SR were greater in the PT than No PT group. Ratings of perceived exertion values were significantly greater in the PT compared with the No PT group for CP, LE, and SR but not LP. These results indicate that resistance training under the supervision of a personal trainer leads to greater initial 1RM strength values, self-selection of greater workout intensities, and greater ratings of perceived exertion values during resistance exercise. 相似文献
159.
Milliken LA Faigenbaum AD Loud RL Westcott WL 《Journal of strength and conditioning research / National Strength & Conditioning Association》2008,22(4):1339-1346
Despite the widespread use of and acceptance of muscular fitness field tests in national youth fitness test batteries, little is known about how these field tests compare to 1 repetition maximum (1RM) strength in children. Therefore, the aim of this study was to characterize and identify correlates of muscular strength in children 7 to 12 years of age. Ninety children (39 girls and 51 boys) between the ages of 6.7 and 12.3 years volunteered to participate in this study. Children were tested on 1RM chest press (CP) strength, 1RM leg press (LP) strength, handgrip strength, vertical jump, long jump, sit and reach flexibility, and height and weight (used to determine body mass index [BMI]). For the combined sample, LP 1RM ranged from 75% to 363% of body weight and CP 1RM ranged from 25% to 103% of body weight. Multiple regression analyses predicting LP 1RM showed that BMI and long jump were significant (R = 44.4% with age and gender not significant) and BMI and vertical jump were significant (R = 40.8% with age and gender not significant). Multiple regression analyses predicting CP 1RM showed that BMI and handgrip strength were significant (R = 58.6% with age and gender not significant). Age and gender alone accounted for 4.6% (not significant) of the variation in LP 1RM and 15.4% (significant) in CP 1RM. In summary, these data indicate that BMI, handgrip strength, long jump, and vertical jump relate to 1RM strength in children and therefore may be useful for assessing muscular fitness in youths. 相似文献
160.
Cadmium induces a heterogeneous and caspase-dependent apoptotic response in <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> 总被引:1,自引:0,他引:1
Nargund AM Avery SV Houghton JE 《Apoptosis : an international journal on programmed cell death》2008,13(6):811-821
The toxic metal cadmium is linked to a series of degenerative disorders in humans, in which Cd-induced programmed cell death
(apoptosis) may play a role. The yeast, Saccharomyces cerevisiae, provides a valuable model for elucidating apoptosis mechanisms, and this study extends that capability to Cd-induced apoptosis.
We demonstrate that S. cerevisiae undergoes a glucose-dependent, programmed cell death in response to low cadmium concentrations, which is initiated within
the first hour of Cd exposure. The response was associated with induction of the yeast caspase, Yca1p, and was abolished in
a yca1Δ mutant. Cadmium-dependent apoptosis was also suppressed in a gsh1Δ mutant, indicating a requirement for glutathione. Other apoptotic markers, including sub-G1 DNA fragmentation and hyper-polarization of mitochondrial membranes, were also evident among Cd-exposed cells. These responses
were not distributed uniformly throughout the cell population, but were restricted to a subset of cells. This apoptotic subpopulation
also exhibited markedly elevated levels of intracellular reactive oxygen species (ROS). The heightened ROS levels alone were
not sufficient to induce apoptosis. These findings highlight several new perspectives to the mechanism of Cd-dependent apoptosis
and its phenotypic heterogeneity, while opening up future analyses to the power of the yeast model system. 相似文献