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71.
Single Doses of Acrylamide Reduce Retrograde Transport Velocity 总被引:4,自引:4,他引:0
Abstract: Single doses of acrylamide (0–1.3 mmol/kg) produced a dose-dependent decrease in the transport of 125 I-tetanus toxin to the perikarya of sensory neurons in dorsal root ganglia and motor neurons in ventral spinal cord. Acrylamide was a more potent inhibitor of retrograde transport in sensory axons than in motor axons. Substantially greater doses of N,N '-methylene-bis-acryl-amide, a reportedly non-neurotoxic analog of acrylamide, were required to alter the axonal transport of 125 I-tetanus toxin. Velocity of retrograde transport was assessed by determining the position of the leading edge of transported125 I-tetanus toxin at times following single doses of acrylamide. Acrylamide reduced the velocity of 125 I-tetanus toxin transport in a dose-dependent manner by up to 75%. No change in neuronal uptake of 125 I-tet-anus toxin was detected. It is concluded that single doses of acrylamide produce profound alterations in retrograde transport which precede the appearance of structural changes in affected nerve fibers. 相似文献
72.
Summary The stability of the plasmid pJDB 248 has been measured in theS. cerevisiae strain S150-2B growing in a chemostat under conditions of glucose limitation. It was found that reducing the growth rate of the culture led to a more rapid loss of the plasmid from the cells. 相似文献
73.
Saturation transfer EPR spectroscopy on spin-labeled muscle fibers using a loop-gap resonator.
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Previously, saturation transfer (ST-EPR) studies of biomolecular dynamics have involved the use of a resonant cavity and the V'2 display (absorption, second harmonic, out of phase). In the present study, we replaced the resonant cavity with a loop-gap resonator and used the U'1 display (dispersion, first harmonic, out of phase) to study spin-labeled muscle fibers. The new resonator and display showed several advantages over those previously used. It produced virtually noiseless U'1 spectra on a 0.4 microliter sample using a 4 min scan; previous U'1 experiments on spin-labeled muscle, using a conventional rectangular cavity, resulted in an unacceptably low signal-to-noise ratio. The high filling factor of the resonator facilitated the study of these extremely small fiber bundles and permitted high microwave field intensities to be achieved at much lower incident microwave power levels, thus greatly enhancing the signal-to-noise ratio in U'1 experiments. This reduction in the noise level made it possible to benefit from the other advantages of U'1 over V'2, such as stronger signals, simpler line shapes, and simpler data analysis. For these muscle fiber samples, the resulting sensitivity (signal/noise/sample volume) of the U'1 signals was greater than 100 times that of V'2 signals obtained in a conventional cavity. Another advantage of the U'1 display is that signals from weakly immobilized probes, i.e., probes that have nanosecond rotational mobility relative to the labeled protein (myosin), are greatly suppressed relative to strongly immobilized probes. This reduces the ambiguity of spectral analysis, and eliminates the need for chemical treatments [e.g., using K3Fe(CN)6] that were previously required in muscle fibers and other systems. Further suppression of this weakly immobilized component was achieved in U'1 spectra by increasing the microwave power and decreasing the field modulation frequency. 相似文献
74.
The pH dependence of hydrogen exchange in proteins 总被引:3,自引:0,他引:3
The static accessibility modified discrete charge model for electrostatic interactions in proteins is extended to the prediction of the pH dependence of hydrogen exchange reactions. The exchange rate profiles of buried amide protons are shown to follow the calculated pH dependence of the electrostatic component of protein stability. Rate profiles are calculated for individual buried amide protons in ribonuclease S and bovine pancreatic trypsin inhibitor. The electrostatic free energy of stabilization of the protein and the energy required to bring the catalytic ion to an exchange site are expressed as an apparent, pH-dependent contribution to the activation energy. Changes in the electrostatic stabilization of the proteins affect the calculated exchange rate for buried amide protons by more than 1000, while local field effects raise or lower the predicted exchange rates by less than 100. The pH dependence of exchangeable protons at the protein surface, such as the C-2 imidazole protons, is shown to follow the estimated energy required to introduce the catalytic ion at the exchange site. These calculations are discussed in terms of current models for proton exchange which incorporate the dynamic nature of the structure to explain exchange data from the interior of a protein. 相似文献
75.
The activities of neutral, magnesium-stimulated, and acid sphingomyelinases were measured in five regions of rat brain. Neutral enzyme activity was 2-3-fold higher in striatum than in parietal cortex and 13-fold higher than in cerebral white matter. Acid sphingomyelinase activity was more evenly distributed throughout these regions. Striatal neutral sphingomyelinase activity was not affected by treatment of rats with reserpine or haloperidol and was reduced (16%) by 6-hydroxydopamine. Striatal acid sphingomyelinase was unaffected by reserpine and 6-hydroxydopamine, and was increased (17%) by haloperidol. We conclude that neutral, magnesium-stimulated sphingomyelinase activity differs in various regions of rat brain and is particularly enriched in the corpus striatum. However, it appears to be a constitutive component of tissue rather than a readily modulated regulatory element of the catecholaminergic system. 相似文献
76.
A transepithelial potential of +8.74±0.29 mV (n = 85) has been recorded across the Malpighian tubules of Locusta. The effect of varying the Na+ and K+ concentration in the bathing medium on the transepithelial potential has been determined. The data show that the transepithelial potential does not obey the Nernst equation for K+. Ouabain, ethacrynic acid and amiloride all inhibit the transepithelial potential. The results are discussed in relation to the nature of the mechanisms of cation transport across the Malpighian tubules. 相似文献
77.
Growth and lipolysis of rat adipose tissue: effect of age, body weight, and food intake 总被引:2,自引:0,他引:2
The purpose of the present work was to study age- and weight-controlled rats to determine which is the primary factor in reducing the lipolytic response of free fat cells and which has the greater effect on the ratio of fat cells to nonfat cells in adipose tissue. The method for estimating fat cell and nonfat cell numbers is based on the analysis of adipose tissue and fat cell DNA and lipid. In adequately fed rats, epididymal adipocyte hyperplasia is complete between 9 and 14 wk of age. Chronic underfeeding delays, but does not eliminate, normal fat cell hyperplasia and is accompanied by a net loss in the nonfat cell population. During 9-14 wk of age, rat epididymal adipose tissue enlarges mainly through adipocyte hypertrophy. Total fat cells from the epididymal adipose tissue of control rats represent only 20-23% of the total cell population. Chronic underfeeding increases the percentage of fat cells in the fat pad from 23 to 28%. Noradrenaline-stimulated lipolysis is proportional to fat cell numbers but is inhibited when fat cell lipid increases to over 80% of fat pad wet weight. Rat age is apparently not primarily responsible for the decreased noradrenaline-stimulated lipolysis in fat cells of 350-g rats in vitro. 相似文献
78.
Colneleic acid is an unsaturated ether fatty acid derived from linoleic acid via a lipoxygenase-mediated enzyme pathway. It is degraded (a) by an enzyme in potato tubers which is heat-labile and non-dialysable and (b) by a model system containing catalytic amounts of Fe(2+) ions. Both enzyme- and Fe(2+)-catalysed systems have similar properties with respect to pH optima (pH5.0-5.5), oxygen requirement (0.6-0.7 mol of O(2) consumed/mol of ether degraded), inhibitors and reaction products. An unstable product breaks down to C(8) and C(9) carbonyl fragments. Both systems are inhibited by low concentrations of antioxidants (e.g. 5mum-butylated hydroxytoluene) and some chelating agents (e.g. 5mum-diethyldithio-carbamate). The model system is strongly inhibited by metal ions, particularly Cu(2+) and Fe(3+), at 20mum. Hydrogen peroxide and haemoproteins do not substitute for the enzyme or Fe(2+) ions but the non-haem iron protein, ferredoxin, does catalyse the degradation. 相似文献
79.
In Vitro Antimicrobial Activity and Human Pharmacology of Cephalexin, a New Orally Absorbed Cephalosporin C Antibiotic 总被引:3,自引:1,他引:2
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Thomas S. Thornhill Matthew E. Levison Warren D. Johnson Donald Kaye 《Applied microbiology》1969,17(3):457-461
Concentrations of cephalexin (an orally absorbed derivative of cephalosporin C) in serum and urine were determined in normal volunteers and patients. The in vitro antibacterial activity was also studied. All strains of group A β-hemolytic streptococci and Diplococcus pneumoniae were inhibited by 3.1 μg/ml. Of the Staphylococcus aureus strains, 88% were inhibited by 6.3 μg/ml, and 12.5 μg/ml was inhibitory for all S. aureus, 80% of Escherichia coli, 72% of Klebsiella-Aerobacter, and 56% of Proteus mirabilis strains. About 90 to 96% of E. coli, Klebsiella Aerobacter, and P. mirabilis strains were inhibited by 25 μg of cephalexin per ml. Pseudomonas and indole-positive Proteus strains proved to be quite resistant to cephalexin. Cephalexin was well absorbed after oral administration. A peak serum concentration of cephalexin of at least 5 μg/ml was achieved in each volunteer with 250 and 500-mg doses. A mean peak serum concentration of 7.7 μg/ml was achieved with 250-mg doses; 12.3μg/ml was achieved with 500-mg doses of antibiotic. Food did not interfere with absorption. Probenecid enhanced both the peak serum concentration and the duration of antibiotic activity in the serum. Over 90% of the administered dose was excreted in the urine within 6 hr. The mean peak serum concentration of cephalexin after an oral dose of 500 mg was adequate to inhibit all group A streptococci, D. pneumoniae, and S. aureus, 85% of E. coli, and about 40 to 75% of Klebsiella-Aerobacter and P. mirabilis strains. Levels of cephalexin in urine were adequate to inhibit over 90% of E. coli, and P. mirabilis and 80 to 96% of Klebsiella-Aerobacter strains. 相似文献
80.