RESUMEN
In a previous article (Yallop and Svendsen 2001), recombinant CHO and BHK cell lines, expressing the human glucagon receptor and the gastric inhibitory peptide receptor, respectively, showed reduced growth rates and altered nutrient utilisation when grown with increasing concentrations of G418. This response was associated with an increased expression of the neo (r) protein, while expression of the recombinant membrane receptors remained unaltered. The metabolic response was characterised in both cell lines by an increase in the specific rate of glutamine utilisation and in CHO cells by a decrease in the yield of lactate from glucose, suggesting a change in the flux of glucose through central metabolism. The aim of this study was to further elucidate these metabolic changes by determining the activity and relative expression of key enzymes involved in glucose and glutamine metabolism. For both CHO and BHK cells, there was an increase in the activity of glutaminase, glutamate dehydrogenase and glutamine synthetase, suggesting an increased flux through the glutaminolysis pathway. The activity of glucose-6-phosphate dehydrogenase and pyruvate carboxylase in CHO cells was also increased whilst lactate dehydrogenase activity remained unaltered, suggesting an increased flux to the pentose phosphate pathway and TCA cycle, respectively. The activity of these enzymes in BHK cells was unchanged. Quantitative RT-PCR showed that expression levels of glutaminase and pyruvate carboxylase were the same with and without G418, indicating that the differences in activities were likely due to post-translational modifications.
RESUMEN
It is widely reported that the growth of recombinant bacteria and yeast is adversely affected by increased metabolic load caused by the maintenance of plasmid copy number and recombinant protein expression. Reports suggest that recombinant mammalian systems are similarly affected by increased metabolic load. However, in comparison to bacterial systems relatively little information exists. It was the aim of this study to test the effects of recombinant gene expression on the growth and metabolism of two industrially important cell lines. A BHK and CHO cell line were stably transfected with the human gastric inhibitory peptide (h-GIP)and glucagon receptor respectively. Selection was by way of the neomycin resistance (neo (r)) gene using G418.The growth and metabolism of both cell lines was affected by the presence of G418 in a manner indicative of increased metabolic load and which appeared to be caused by over-expression of the neomycin resistance protein. The two cell lines differed in their metabolic response to G418, which suggested that some cell lines or clones may be better able to tolerate a metabolic load than others. Growth under increased metabolic load was affected by medium composition with serum, insulin and glutamine concentration as influencing factors. Implications for the use of G418 are discussed.
RESUMEN
A total of 34 thermophilic isolates identified as members of the genus Thermoactinomyces by a range of chemotaxonomic, microscopic and determinative biochemical tests, were isolated from two acid soils. Growth studies in shake flask and fermenter identified the isolates to be moderately acidophilic with growth occurring between pH 4.5 and 6.0 with optima at pH 5.0. The isolates differed considerably from known Thermoactinomyces cultures in their pH profile, colony morphology and in several biochemical tests. Extracellular enzyme activities are identified and partially characterized in terms of their thermostability, pH and temperature profiles from crude supernatant fluid samples. Optimal protease, amylase and pullulanase activity was observed at pH 5.0-5.5 and 75-80 degrees C with each showing T(50) values of 10, 30 and 30 min, respectively. A highly thermotolerant extracellular esterase was also identified which retained 50% activity after 8 h at 90 degrees C. This is the first report of an acidophilic member of the genus Thermoactinomyces.
Asunto(s)
Actinomycetales/aislamiento & purificación , Actinomycetales/enzimología , Actinomycetales/crecimiento & desarrollo , Concentración de Iones de Hidrógeno , TemperaturaRESUMEN
Extracellular esterases have so far only been reported in eubacteria, here we report the first identification and partial characterisation of a novel inducible extracellular esterase from the thermoacidophilic archaeon Sulfolobus shibatae. This esterase exhibits remarkable stability to both acid and heat. Esterase activity is induced by growth on a range of polyoxyethylenesorbitan (Tween) compounds as sole carbon source. Activity occurs over a wide temperature (25-99 degrees C) and pH (pH4.0-9.0) range and is optimal at 90 degrees C and pH6.0. It exhibits high thermal stability, with a half-life of 20 min at 120 degrees C, and shows a transient thermal activation of 60% at 90 degrees C. The thermal inactivation of function occurs by first order kinetics, and after 120 min incubation at 120 degrees C 50% of activity still remains. It is able to hydrolyse mono- and diglycerides, but is unable to hydrolyse the triglycerides olive oil and triolein, which is indicative of an esterase and not a lipase.
Asunto(s)
Esterasas/química , Esterasas/metabolismo , Sulfolobus/enzimología , Inducción Enzimática , Estabilidad de Enzimas , Esterasas/biosíntesis , Calor , Concentración de Iones de Hidrógeno , Cinética , Lipasa/biosíntesis , Lipasa/química , Lipasa/metabolismo , Polisorbatos/farmacología , Factores de TiempoRESUMEN
Actinomycetes are widespread in the environment and are mainly organotrophic. Studies of their ecology have been primarily focussed on their detection and isolation, with comparatively little attention to the control mechanisms that determine their occurrence and behaviour in their natural environments. This session provided some diverse examples of approaches to this problem. Several actinomycete genera produce motile spores. The significance of flagella proteins and factors influencing spore motility and germination are considered. The genus Frankia forms nitrogen-fixing associations with non-leguminous plants. Molecular techniques have been used to clarify the endophyte-host relationships. Micromonospora species are common in the environment. The growth and physiology of a gentamicin-producing strain are described. Thermophilic actinomycetes in the genus Thermoactinomyces are common in composts and other self-heating environments. Novel isolates from acid soil, which grow and produce enzymes active at high temperatures and in acidic conditions, are discussed.