Glutamine-dependent Asparagine Synthetase from Leukemia Cells

Asparagine synthetase, purified from an asparaginase-resistant mouse leukemia (RADA1), catalyzes the formation of l-asparagine, AMP, PPi, and l-glutamate from l-aspartate, l-glutamine, and ATP. l-Glutamine may be replaced by NH4+ as the amide nitrogen donor. The postulated intermediate, β-l-aspartyl adenylate, was prepared by organic synthesis. The enzyme catalyzes the synthesis of ATP from PPi and β-l-aspartyl adenylate. Asparagine synthetase was found to exhibit glutaminase activity both in the presence and absence of the other substrates needed for asparagine synthesis. Both the glutaminase and glutamine-dependent (but not the NH4+-dependent) synthetase activities require chloride ions; Cl- can be replaced by Br- or I-, but with much less activity. The enzyme is inhibited by l-2-amino-4-oxo-5-chloropentanoic acid (which binds, probably covalently, to the enzyme), aminomalonic acid, N-methyl-dl-aspartic acid, and several other compounds. These compounds or similar ones may be useful in augmenting asparaginase therapy of tumors.