Soluble asparaginase-dextran conjugates show increased circulatory persistence and lowered antigen reactivity

Oxidized dextrans of increasing molecular weight were bound covalently to Erwinia carotovora asparaginase. The resulting conjugates retained 50% of their enzyme activity and showed marked resistance to proteolysis by trypsin and chymotrypsin and inactivation by asparaginase-specific antibody. When tested in-vivo, the larger molecular weight conjugates showed prolonged circulatory survival in both immune and non-immune animals and failed to elicit full type III hypersensitivity or anaphylactic reactions when injected into sensitized guinea-pigs. Rabbits could tolerate multiple doses of the asparaginase conjugate without developing an immunity to the enzyme. A conjugate showing increased circulatory half-life and lowered antigen reactivity should have therapeutic potential.