ISSN:
1471-4159
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
Abstract: A sensitive radioisotopic assay has been used to examine the kinetic properties and regulation of biosynthesis of glutamine synthetase in C-6 glioma cultures. The Km values for glutamate, MgATP, and ammonium ion were 5mM, 14 mM, and 0.042 mM, respectively, when measured at the pH optimum of 7.2. There was an absolute requirement for a divalent metal ion, with 15 mM- Mg2+ being the preferred ion at pH 7.2. Activity was completely inhibited after 30 min with 8 mM-L-methionhe sulfoximine. The addition of 1 μM-cortisol to C-6 cultures caused a two to threefold increase in glutamine synthetase specific activity over a 96-h period, while dexamethasone at the same concentration elevated the level some 7-10-fold. This was specific for glucocorticoids, as other steroid hormones or catecholamines did not significantly affect glutamine synthetase specific activity. Cycloheximide (30 μM) or actinomycin D (0.01 μg/ml) blocked the hormone response. The continued presence of hormone was required in order to maintain an elevated enzyme level. The results suggest that glucocorticoids act to induce glutamine synthetase by stimulating new enzyme synthesis.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1471-4159.1980.tb09659.x
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