L-ASPARAGINYL-TRANSFER RNA-SYNTHETASE AND L-ASPARAGINE SYNTHETASE ACTIVITIES OF L-ASPARAGINASE-SENSITIVE AND L-ASPARAGINASE-RESISTANT FORMS OF THE MOUSE GARDNER LYMPHOMA 6C3HED

The mouse Gardner lymphoma 6C3HED was grown in ascites fluid in a form sensitive to the action of L-asparaginase (line 1), in another form which was resistant to L-asparaginase (line 2) and in a 3rd form with partial sensitivity to L-asparaginase (line 3). The L-asparaginyl-tRNA synthetase activities of extracts of the tumor cells, cultured in the mouse and in vitro, were determined. Lines 1 and 3, in early passage numbers, showed a derepression mechanism involving L-asparagine. Mutation occurred with these lines, resulting in the L-asparaginyl-tRNA synthetase activity of all the tumor cell lines being the same. Cells of line 1 had low L-asparagine synthetase activity, which was unchanged by altering the supply of L-asparagine in vitro. Cells of lines 2 and 3 exhibited L-asparagine synthetase activities, which changed with the supply of L-asparagine. It is not certain that L-asparagine synthetase activity of L-asparaginase-sensitive cells is controlled by L-asparaginyl-tRNA acting as a corepressor. [L-asparaginase has been used as treatment for patients with lymphocytic leukemia.].