Effects of glutamine on the two catalytic activities of glutamine synthetase in cultured mouse cells strain L

When cultured mouse cells strain L are incubated in the presence of glutamine (normally a component of their growth medium) both the transferase (γ-glutamyl transfer) and the synthetase (acyl activation) activities of glutamine synthetase are equally depressed, the transferase being on the whole 5 times higher than the synthetase activity. Whereas the depressive action of glutamine is established within 24 hours, the increase in enzymatic activity following withdrawal of glutamine is markedly slower. The action of glutamine involves two mechanisms, neither of which requires protein or RNA synthesis: (a) inhibition of the synthesis of glutamine synthetase; and (b) promotion of destruction of preexisting enzyme or complements of it.