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121.
In amino acid production by coryneform bacteria, study on relationship between change in enzyme activities and production of a target amino acid is important. In glutamate production, Kawahara et al. discovered that the effect of decrease in 2-oxoglutamate dehydrogenase complex (ODHC) on glutamate production is essential (Kawahara et al., Biosci. Biotechnol. Biochem. 61(7) (1997) 1109). Significant reduction of the ODHC activity was observed in the cells under the several glutamate-productive conditions in Corynebacterium glutamicum. Recent progress in metabolic engineering enables us to quantitatively compare the flux redistribution of the different strains after change in enzyme activity precisely. In this paper, relationship between flux redistribution and change in enzyme activities after biotin deletion and addition of detergent (Tween 40) was studied in two coryneform bacteria, C. glutamicum and a newly isolated strain, Corynebacterium efficiens (Fudou et al., Int. J. Syst. Evol. Microbiol. 52(Part 4) 1127), based on metabolic flux analysis (MFA). It was observed that in both species the specific activities of isocitrate dehydrogenase (ICDH) and glutamate dehydrogenase (GDH) did not significantly change throughout the fermentation, while that of the ODHC significantly decreased after biotin depletion and Tween 40 addition. Flux redistribution clearly occurred after the decrease in ODHC specific activity. The difference in glutamate production between C. glutamicum and C. efficiens was caused by the difference in the degree of decrease in ODHC specific activity. The difference in Michaelis-Menten constants or K(m) value between ICDH, GDH, and ODHC explained the mechanism of flux redistribution at the branch point of 2-oxoglutarate. It was found that the K(m) values of ICDH and ODHC were much lower than that of GDH for both strains. It was quantitatively proved that the ODHC plays the most important role in controlling flux distribution at the key branch point of 2-oxoglutarate in both coryneform bacteria. Flux redistribution mechanism was well simulated by a Michaelis-Menten-based model with kinetic parameters. The knowledge of the mechanism of flux redistribution will contribute to improvement of glutamate production in coryneform bacteria.  相似文献   
122.
It is known that skin often shows irregular pigmentation during aging, which is frequently associated with hyperpigmentation. Many studies have utilized brownish A1 guinea pigs to investigate the pathogenesis of ultraviolet B (UVB)-induced skin pigmentation, however, responses associated with aging following UVB irradiation have not been elucidated. To characterize those responses, dorsal skin of A1 guinea pigs from 14-weeks to 5-yr old were investigated. The minimal erythema dose was found to increase with aging. Further, in pigmentation induced by UVB radiation, skin brightness (DeltaL*-value) decreased equally in both the 14-week old (young) group and in the 3-yr old (old) group of guinea pigs. The DeltaL*-value recovered in the young group from 21 d after UVB irradiation, whereas no such recovery was seen in the old group. In addition, the amount of melanin and the number of melanocytes returned near pre-irradiation levels in the young group, while they remained high in the old group. Our results therefore demonstrate for the first time that skin responses following UVB irradiation change with aging in A1 guinea pigs.  相似文献   
123.
We analyzed Polycomb group gene ph2alpha functionally in zebrafish embryos by a gene knock-down procedure using morpholino antisense oligos. Inhibition of ph2alpha message translation resulted in abnormal epibolic movements as well as a thick tailbud or incomplete covering of the yolk plug. At the 24hpf stage, morphants had short trunks and tails, phenotypes similar to those with disturbances in FGF signaling. Accordingly, we looked at the effects of ph2alpha expression upstream and downstream of the FGF pathway. Treatment with SU5402, an inhibitor of Fgfrs, or injection of dominant-negative Fgfr1 DNA markedly reduced ph2alpha expression in the tailbud. In addition, cells expressing mRNAs for no tail, spadetail, myoD, and papc, which are involved in FGF-related development of posterior mesoderm, were distributed abnormally. Collectively, the data argue that ph2alpha is required for epiboly and tailbud formation, acting downstream of the FGF signaling pathway.  相似文献   
124.
We examined whether starvation during the initial period of life in stem females affected reproductive characteristics of the offspring. Starvation treatment had different effects on rotifers hatched from resting eggs and those hatched from amictic eggs. When stem females experienced starvation after hatching, this induced a higher percentage of mixis in their offspring. When the same starvation treatment was applied to rotifers hatched from amictic eggs, there was no effect on the induction of mixis. It is probable that stem females hatched from resting eggs have specific features that are vulnerable to unfavorable environmental conditions, and that these features can be inherited by their offspring through the maternal cytoplasm.  相似文献   
125.
Parasitoids and predatory flies were sampled in the wheat production region of the west-central Great Plains (southeastern Wyoming, western Nebraska, and north-central Colorado) of North America using plant material infested with the Russian wheat aphid, Diuraphis noxia (Mordvilko) (Hemiptera: Aphididae). Samples were taken April through October in 2001 and 2002, which was 15–16 years after first detection of D. noxia and 5–6 years after the last release of natural enemies for its control in this region. The natural enemies detected were (in order of high to low detection frequencies across three states and 2 years): Aphelinus albipodus Hayat and Fatima (Hymenoptera: Aphelinidae), Eupeodes volucris Osten Sacken (Diptera: Syrphidae), Lysiphlebus testaceipes (Cresson) (Hymenoptera: Braconidae, Aphidiinae), Leucopis gaimarii Tanasijtshuk (Diptera: Chamaemyiidae), Aphidius avenaphis (Fitch), Aphidius matricariae Haliday, Diaeretiella rapae (MIntosh), Aphidius ervi Haliday, Praon yakimanum Pike and Starý (Hymenoptera: Braconidae, Aphidiinae), and Aphelinus asychis Walker (Hymenoptera: Aphelinidae). The results confirmed establishment of one of the 10 exotic parasitoid species released for D. noxia control (A. albipodus) in the west-central Great Plains. It is unknown whether detection of A. asychis, A. matricariae, and D. rapae can be attributed to exotic introductions or preexisting populations. Other species detected in this study have been previously documented from the western US, although the recognized distributions have expanded for A. avenaphis, L. gaimarii, and P. yakimanum compared to the first few years after initial detection of D. noxia. Thus, there is definitive establishment of one exotic introduced for D. noxia and considerable range expansion of preexisting species that prey upon D. noxia.  相似文献   
126.
The class II and class I chitin synthases of the filamentous fungus Aspergillus nidulans are encoded by chsA and chsC, respectively. Previously, we presented several lines of evidence suggesting that ChsA and ChsC have overlapping functions in maintaining cell wall integrity. In order to determine the functions of these chitin synthases, we employed electron and fluorescence microscopy and investigated in detail the cell wall of a DeltachsA DeltachsC double mutant (DeltaAC mutant) along with the localization of ChsA and ChsC. In the lateral cell wall of the DeltaAC mutant, electron-transparent regions were thickened. Septa of the DeltaAC mutant were aberrantly thick and had a large pore. Some septa were located abnormally close to adjacent septa. A functional hemagglutinin (HA)-tagged ChsA (HA-ChsA) and a functional FLAG-tagged ChsC (FLAG-ChsC) were each localized to a subset of septation sites. Comparison with the localization pattern of actin, which is known to localize at forming septa, suggested that ChsA and ChsC transiently exist at the septation sites during and shortly after septum formation. Double staining of HA-ChsA and FLAG-ChsC indicated that their localizations were not identical but partly overlapped at the septation sites. Fluorescence of FLAG-ChsC, but not of HA-ChsA, was also observed at hyphal tips. These data indicate that ChsA and ChsC share overlapping roles in septum formation.  相似文献   
127.
The cAMP receptor protein SYCRP1 in cyanobacterium Synechocystis sp. PCC 6803 is a regulatory protein that binds to the consensus DNA sequence (5'-AAATGTGATCTAGATCACATTT-3') for the cAMP receptor protein CRP in Escherichia coli. Here we examined the effects of systematic single base-pair substitutions at positions 4-8 (TGTGA) of the consensus sequence on the specific binding of SYCRP1. The consensus sequence exhibited the highest affinity, and the effects of base-pair substitutions at positions 5 and 7 were the most deleterious. The result is similar to that previously reported for CRP, whereas there were differences between SYCRP1 and CRP in the rank order of affinity for each substitution.  相似文献   
128.
Saito K  Oda M  Sarai A  Azuma T  Kozono H 《Biochemistry》2004,43(31):10186-10191
We used differential scanning calorimetry to study the thermal denaturation of murine major histocompatibility complex class II, I-E(k), accommodating hemoglobin (Hb) peptide mutants possessing a single amino acid substitution of the chemically conserved amino acids buried in the I-Ek pocket (positions 71 and 73) and exposed to the solvent (position 72). All of the I-Ek-Hb(mut) molecules exhibited greater thermal stability at pH 5.5 than at pH 7.4, as for the I-Ek-Hb(wt) molecule, which can explain the peptide exchange function of MHC II. The thermal stability was strongly dependent on the bound peptide sequences; the I-Ek-Hb(mut) molecules were less stable than the I-Ek-Hb(wt) molecules, in good correlation with the relative affinity of each peptide for I-Ek. This supports the notion that the bound peptide is part of the completely folded MHC II molecule. The thermodynamic parameters for I-Ek-Hb(mut) folding can explain the thermodynamic origin of the stability difference, in correlation with the crystal structural analysis, and the limited contributions of the residues to the overall conformation of the I-Ek-peptide complex. We found a linear relationship between the denaturation temperature and the calorimetric enthalpy change. Thus, although the MHC II-peptide complex could have a diverse thermal stability spectrum, depending on the amino acid sequences of the bound peptides, the conformational perturbations are limited. The variations in the MHC II-peptide complex stability would function in antigen recognition by the T cell receptor by affecting the stability of the MHC II-peptide-T cell receptor ternary complex.  相似文献   
129.
When any muscle in the human musculoskeletal system is damaged, other muscles and ligaments tend to compensate for the role of the damaged muscle by exerting extra effort. It is beneficial to clarify how the roles of the damaged muscles are compensated by other parts of the musculoskeletal system from the following points of view: From a clinical point of view, it will be possible to know how the abnormal muscle and joint forces caused by the acute compensations lead to further physical damage to the musculoskeletal system. From the viewpoint of rehabilitation, it will be possible to know how the role of the damaged muscle can be compensated by extra training of the other muscles. A method to evaluate the influence of muscle deactivation on other muscles and joints is proposed in this report. Methodology based on inverse dynamics and static optimization, which is applicable to arbitrary motion was used in this study. The evaluation method was applied to gait motion to obtain matrices representing (1) the dependence of muscle force compensation and (2) the change to bone-on-bone contact forces. These matrices make it possible to evaluate the effects of deactivation of one of the muscles of the musculoskeletal system on the forces exerted by other muscles as well as the change to the bone-on-bone forces when the musculoskeletal system is performing the same motion. Through observation of this matrix, it was found that deactivation of a muscle often results in increment/decrement of force developed by muscles with completely different primary functions and bone-on-bone contact force in different parts of the body. For example, deactivation of the iliopsoas leads to a large reduction in force by the soleus. The results suggest that acute deactivation of a muscle can result in damage to another part of the body. The results also suggest that the whole musculoskeletal system must go through extra retraining in the case of damage to certain muscles.  相似文献   
130.
Cyclin-dependent kinase 5 (Cdk5) is emerging as a neuronal protein kinase involved in multiple aspects of neurotransmission in both post- and presynaptic compartments. Within the reward/motor circuitry of the basal ganglia, Cdk5 regulates dopamine neurotransmission via phosphorylation of the postsynaptic signal transduction pathway integrator, DARPP-32 (dopamine- and cyclic AMP-regulated phosphoprotein, M(r) 32,000). Cdk5 has also been implicated in regulating various steps in the presynaptic vesicle cycle. Here we report that Cdk5 phosphorylates tyrosine hydroxylase (TH), the key enzyme for synthesis of dopamine. Using phosphopeptide mapping, site-directed mutagenesis, and phosphorylation state-specific antibodies, the site was identified as Ser31, a previously defined extracellular signal-regulated kinases 1/2 (ERK1/2) site. The phosphorylation of Ser31 by Cdk5 versus ERK1/2 was investigated in intact mouse striatal tissue using a pharmacological approach. The results indicated that Cdk5 phosphorylates TH directly and also regulates ERK1/2-dependent phosphorylation of TH through the phosphorylation of mitogen-activated protein kinase kinase 1 (MEK1). Finally, phospho-Ser31 TH levels were increased in dopaminergic neurons of rats trained to chronically self-administer cocaine. These results demonstrate direct and indirect regulation of the phosphorylation state of a Cdk5/ERK1/2 site on TH and suggest a role for these pathways in the neuroadaptive changes associated with chronic cocaine exposure.  相似文献   
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