Biosynthesis Rates (biosynthesis + rate)

Distribution by Scientific Domains

Selected Abstracts

Ecdysteroid synthesis and imaginal disc development in the midge Chironomus riparius as biomarkers for endocrine effects of tributyltin

Torsten Hahn
Abstract Acute effects of the endocrine disruptor bis (tri- n -butyltin) oxide (TBTO) on molting-hormone biosynthesis and imaginaldisc development were investigated in larvae of the midge Chironomus riparius (Meigen). Ecdysteroid synthesis was measured by 24-h incubation of molting-hormone-synthesizing tissues (prothoracic glands) in vitro with or without the addition of TBTO. The amount of ecdysteroids produced was analyzed by radioimmunoassay. Developmental effects in vivo were investigated by determining the developmental phase of the genital imaginal discs before and after a 48-h exposure to TBTO in water. Sex-specific effects were found with both endpoints. Ecdysteroid synthesis was significantly reduced (analysis of variance [ANOVA], p , 0.005) in female larvae at all concentrations (TBTO-Sn at 50, 500, and 5,000 ng/L), whereas a significant elevation of the biosynthesis rate occurred in male larvae in the 500-ng/L treatment (ANOVA, p , 0.05). In vivo experiments with development of the genital imaginal disc within a 48-h exposure period revealed a significantly slower development in female larvae and a significantly faster development in male larvae (contingency tables, p , 0.001) at all concentrations tested (TBTO-Sn at 10, 50, 200, and 1,000 ng/L). These results partly coincided with the in vitro effects on molting-hormone synthesis. The 48-h median lethal concentration (LC50) was 25 ,g/L (20,30 ,g/L 95% confidence intervals). The combination of in vitro and in vivo methods has proven to be a useful approach for the detection of endocrine effects of TBTO in C. riparius at levels 2,000-fold below the LC50 value. High sensitivity and short test duration suggest that chironomids may have potential as freshwater sentinel organisms for endocrine-disrupting chemicals. [source]

Intervertebral disc cell response to dynamic compression is age and frequency dependent,

Casey L. Korecki
Abstract The maintenance of the intervertebral disc extracellular matrix is regulated by mechanical loading, nutrition, and the accumulation of matrix proteins and cytokines that are affected by both aging and degeneration. Evidence suggests that cellular aging may lead to alterations in the quantity and quality of extracellular matrix produced. The aims of this study were to examine the role of loading and maturation (a subset of aging), and the interaction between these two factors in intervertebral disc cell gene expression and biosynthesis in a controlled 3D culture environment. Cells were isolated from young (4,6 months) and mature (18,24 months) bovine caudal annulus fibrosus and nucleus pulposus tissue. Isolated cells were seeded into alginate and dynamically compressed for 7 days at either 0.1, 1, or 3 Hz or maintained as a free-swelling control. After 7 days, DNA and sulfated glycosaminoglycan contents were analyzed along with real time, quantitative reverse transcription-polymerase chain reaction analysis for collagen types I and II, aggrecan, and matrix metalloproteinase-3 gene expression. Results suggest that maturation plays an important role in intervertebral disc homeostasis and influences the cell response to mechanical loading. While isolated intervertebral disc cells responded to mechanical compression in 3D culture, the effect of loading frequency was minimal. Altered cellular phenotype and biosynthesis rates appear to be an attribute of the cell maturation process, potentially independent of changes in cellular microenvironment associated with lost nutrition and disc degeneration. Mature cells may have a decreased capacity to create or retain extracellular matrix components in response to mechanical loading compared to young cells. 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27: 800,806, 2009 [source]

Does engineering abscisic acid biosynthesis in Nicotiana plumbaginifolia modify stomatal response to drought?

C. Borel
ABSTRACT The consequences of manipulating abscisic acid (ABA) biosynthesis rates on stomatal response to drought were analysed in wild-type, a full-deficient mutant and four under-producing transgenic lines of N. plumbaginifolia. The roles of ABA, xylem sap pH and leaf water potential were investigated under four experimental conditions: feeding detached leaves with varying ABA concentration; injecting exogenous ABA into well-watered plants; and withholding irrigation on pot-grown plants, either intact or grafted onto tobacco. Changes in ABA synthesis abilities among lines did not affect stomatal sensitivity to ABA concentration in the leaf xylem sap ([ABA]xyl), as evidenced with exogenous ABA supplies and natural increases of [ABA]xyl in grafted plants subjected to drought. The ABA-deficient mutant, which is uncultivable under normal evaporative demand, was grafted onto tobacco stock and then presented the same stomatal response to [ABA]xyl as wild-type and other lines. This reinforces the dominant role of ABA in controlling stomatal response to drought in N. plumbaginifolia whereas roles of leaf water potential and xylem sap pH were excluded under all studied conditions. However, when plants were submitted to soil drying onto their own roots, stomatal response to [ABA]xyl slightly differed among lines. It is suggested, consistently with all the results, that an additional root signal of soil drying modulates stomatal response to [ABA]xyl. [source]

Error propagation from prime variables into specific rates and metabolic fluxes for mammalian cells in perfusion culture

Chetan T. Goudar
Abstract Error propagation from prime variables into specific rates and metabolic fluxes was quantified for high-concentration CHO cell perfusion cultivation. Prime variable errors were first determined from repeated measurements and ranged from 4.8 to 12.2%. Errors in nutrient uptake and metabolite/product formation rates for 5,15% error in prime variables ranged from 8,22%. The specific growth rate, however, was characterized by higher uncertainty as 15% errors in the bioreactor and harvest cell concentration resulted in 37.8% error. Metabolic fluxes were estimated for 12 experimental conditions, each of 10 day duration, during 120-day perfusion cultivation and were used to determine error propagation from specific rates into metabolic fluxes. Errors of the greater metabolic fluxes (those related to glycolysis, lactate production, TCA cycle and oxidative phosphorylation) were similar in magnitude to those of the related greater specific rates (glucose, lactate, oxygen and CO2 rates) and were insensitive to errors of the lesser specific rates (amino acid catabolism and biosynthesis rates). Errors of the lesser metabolic fluxes (those related to amino acid metabolism), however, were extremely sensitive to errors of the greater specific rates to the extent that they were no longer representative of cellular metabolism and were much less affected by errors in the lesser specific rates. We show that the relationship between specific rate and metabolic flux error could be accurately described by normalized sensitivity coefficients, which were readily calculated once metabolic fluxes were estimated. Their ease of calculation, along with their ability to accurately describe the specific rate-metabolic flux error relationship, makes them a necessary component of metabolic flux analysis. 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source]