L-Asparaginase: Proteins and Enzymes

Asparaginase is an enzyme purified from E. coli and Erwinia carotovora. It acts by deaminating extracellular L asparagine, an amino acid that appears to be essential for protein synthesis by some tumour cells which are unable to synthesise asparagine. Asparaginase from Erwinia carotovora is serologically and biochemically distinct from asparaginase from E. coli, although its antineoplastic activity and toxicity is similar. Asparaginase is usually considered to be cell cycle phase nonspecific, but it may block some cells in G1 or S phase. Asparaginase reduces cellular and humoral immunity. E.coli contains two L asparaginase isoenzymes: L asparaginase I, a low affinity enzyme located in the cytoplasm, and L asparaginase II, a high affinity secreted enzyme.