Thesis

Cell density dependent stimulation of glutamine synthetase activityin cultured mouse teratoma cells

A density dependent stimulation of glutamine synthetase activity (GS) has been observed in cultures of mouse teratoma cells. GS specific activity increases as cultures approach confluency to a level greater than twofold over the basal level found in sparse cultures. After confluency the GS specific activity returns to the basal level found in sparse cultures. The stimulation could not be attributed to age of cultures, medium or glutamine depletion, cell leakage of GS, or change in the amount of cellular protein. Dibutyryl cyclic-AMP plus theophyline repressed GS activity both in cultured teratoma and in teratoma obtained from ascites grown tumors The evidence suggests that the stimulation is contact mediated. The stimulation is prevented by cycloheximide

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