13,395 research outputs found
Yeast hydrolysate as a low-cost additive to serum-free medium for the production of human thrombopoietin in suspension cultures of Chinese hamster ovary cells
No full textTo enhance the performance of a serum-free medium (SFM) for human thrombopoietin (hTPO) production in suspension cultures of recombinant Chinese hamster ovary (rCHO) cells, several low-cost hydrolysates such as yeast hydrolysate (YH), soy hydrolysate, wheat gluten hydrolysate and rice hydrolysate were tested as medium additives. Among various hydrolysates tested, the positive effect of YH on hTPO production was most significant. When 5 g l(-1) YH was added to SFM, the maximum hTPO concentration in batch culture was 40.41 mug ml(-1), which is 11.5 times higher than that in SFM without YH supplementation. This enhanced hTPO production in YH-supplemented SFM was obtained by the combined effect of enhanced q(hTPO) (the specific rate of hTPO production). The supplementation of YH in SFM increased q(hTPO) by 294% and extended culture longevity by >2 days if the culture was terminated at a cell viability of 50%. Furthermore, cell viability throughout the culture using YH-supplemented SFM was higher than that using any other hydrolysate-supplemented SFM tested, thereby minimizing degradation of hTPO susceptible to proteolytic degradation. In addition, YH supplementation did not affect in vivo biological activity of hTPO. Taken together, the results obtained demonstrate the potential of YH as a medium additive for hTPO production in serum-free suspension cultures of rCHO cells
Stability and blood partition of YH-439: A new hepatoprotective agent
No full textThe stability of YH-439 in solutions of various pH, rabbit plasma, rabbit blood, human gastric juice, and rabbit liver homogenates; and its blood partition characteristics between human and rabbit plasma and blood cells were studied by using high-performance liquid chromatography YH-439 seemed to be stable in rabbit plasma, rabbit whole blood, rabbit liver homogenates and solutions ranging in pH from 1 to 9. However, YH-439 was unstable in solutions with pH ranging from 10 to 13. The disappearance half-lives of the compound were 198, 31.1, 6.9 and 4.9 h for the solutions of pH 10, 11, 12 and 13, respectively. Up to 16.2% of YH-439 was destroyed after 4 h incubation with three human gastric juices having pH ranging from 1.5-8.0. This indicates that YH-439 is degraded by enzymes present in gastric juice since YH-439 was stable in enzyme-free solutions in that pH range. YH-439 equilibrated rapidly between plasma and blood cells, and the equilibrium plasma to blood cells concentration ratio was independent of the initial YH-439 blood concentration. The mean values for the plasma to blood cell concentration were 1.46-3.06 and 5.90-14.4 for three rabbit and three human blood samples, respectively, with initial YH-439 blood concentrations in the range 1-20 μg/ml. There was no in vivo and in vitro 'blood storage effect' observed with YH-439.N
Factors influencing the protein binding of YH‐439 using an equilibrium dialysis technique - A new hepatoprotective agent
No full textVarious factors influencing the plasma protein binding of YH-439 to 4% human serum albumin (HSA) were evaluated using the equilibrium dialysis method at the initial YH-439 concentration of 2 mu g mL(-1). It took approximately 12 h of incubation to reach an equilibrium between 4% HSA and isotonic phosphate buffer of pH 7.4 containing 3% of dextran ('the buffer') using a Spectra/Por 2 membrane (molecular weight cut-off, 12000-14000) in a water bath shaker kept at 37 degrees C and at a rate of 50 oscillations min(-1). YH-439 was fairly stable both in 4% HSA and in the 'buffer' for up to 24 h incubation. The binding of YH-439 to 4% HSA was constant (974 +/- 0.55%) at YH-439 concentrations ranging from 0.5 to 10 mu g mL(-1). However, the extent of binding was dependent on HSA concentrations: the values were 90.7, 94.7, 96.7, 97.0, 97.0, 97.1, and 97.5% at HSA concentrations of 0.5, 1, 2, 3, 4, 5, and 6%, respectively. The plasma protein binding decreased with increasing incubation temperature: the binding values were 98.2, 97.6, 97.2, and 96.8% when incubated at 10, 21, 26, and 37 degrees C, respectively. The binding of YH-439 was also influenced by the chloride concentration in the buffer: the binding values were 94.5, 97.0, and 96.8% for the chloride concentrations of 0, 0.249, and 0.546%, respectively. The binding of YH-439 was also dependent on the buffer pH: the percentages of free fraction were 6.0, 4.1, 3.8, 2.8, 2.7 and 2.8% for the buffer pHs of 5.0, 6.0, 6.5, 7.0, 7.4, and 8.0, respectively. The free fraction of YH-439 was slightly increased by the addition of heparin (up to 40 U mL(-1)), sodium azide (NaN3, up to 0.5%), and its metabolites. The protein binding of YH-439 was influenced neither by AAG, acetylsalicylic acid, or sulphisoxazole, nor by the addition of citrate or EDTA. The free fractions of YH-439 in rabbit (4.2%) and dog (4.7%) plasma seemed to be higher than in rats (2.9%) and humans (3.1%).N
Escherichia coli rnpB promoter mutants altered in stringent response
No full textThe promoter of the rnpB gene (encoding the RNA component of Escherichia coli RNase P) shares a consensus discriminator sequence, located between the -10 hexamer sequence and the transcription start site, with other promoters whose activities are repressed upon stringent condition. Under stringent conditions induced by seryl-tRNA starvation the transcription of the rnpB gene was repressed in wild type E. coli but not in a relaxed strain carrying a relA(-) mutation. Site-directed mutagenesis was carried out to examine sequences of the rnpB promoter necessary for stringent control. The results indicate that the discriminator region is responsible for the transcription repression of the rnpB gene during the stringent response and that both the content and position of GC pairs in the region determine the strength of negative stringent signals. (C) 1997 Academic Pres
Yeast Hydrolysate as a Low-cost Additive to Serum-free Medium for the Production of Human Thrombopoietin in Suspension Cultures of Chinese Hamster Ovary Cells
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Periodic and Aperiodic Task Scheduling in Strongly Partitioned Integrated Real-Time Systems
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A TIGHT-BINDING MOLECULAR-DYNAMICS STUDY OF THE EQUILIBRIUM STRUCTURES OF SMALL SI CLUSTERS
No full textWe present the results of tight-binding molecular dynamics calculations for studying the equilibrium structures and the bonding properties of Si-n clusters for n up to 18. To prevent unphysically large charge transfer between different atoms in clusters, we employ the atomic charge neutrality constraint that each atom has approximately four valence electrons. With a limited number of parameters in the tight-binding scheme, the structures of minimum energy are well reproduced, as compared with results from previous ab initio quantum mechanical calculations. We find the abundant cluster sizes n = 4, 7 and 10, which are in good agreement with other theoretical and experimental results. For n greater than or equal to 7, surface-like compact structures with a pentagon or a hexagon base are found to be energetically favourable, resulting in the metallic nature of the cluster bonding, while a core-based structure appears first for Si-15
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