Acrylic microspheres in vivo. II. The effect in rat of L-asparaginase given in microparticles of polyacrylamide.

L-Asparaginase was immobilized in spherical microparticles of polyacrylamide. Particles of three different sizes, mean diameter 0.34, 18 and 36 micron, respectively, were used. The Michaelis constant Km, for L-asparaginase, immobilized in small particles (0.34 micron), is virtually the same as in solution. L-Asparaginase in microparticles was also more stable than free enzyme after storage for 140 days at +4 and +37 degrees C. After an i.v. injection of 200 I.U./kg into rat, the plasma L-asparagine fell to very low values (less than 10 nmol/ml), but was normalized again after 4 to 5 days with both the native and immobilized enzymes. After an i.p. injection of 1000 I.U./kg into rats, the microparticles containing L-asparaginase lowered the plasma L-asparagine level for a substantially longer period of time than L-asparaginase in free solution. Normal L-asparagine level was thus reached on day 14 after the injection with immobilized enzyme. However, L-asparaginase activity was still present in the abdominal lymph nodes after this period of time.