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L-Asparaginase from Escherichia coli was immobilized by entrapment in a gel based on poly(2-hydroxyethyl methacrylate) with an activity as high as 730 I.U./g of dry gel. The apparent Michaelis constant for these gels was similar to that of the free enzyme. At 37 degrees C the immobilized enzyme had a half-life of more than 40 days, in vitro. The gel was freeze-dried, crushed and sieved to pass a 38 mum screen, giving a median particle size of 12 mum. C3H mice were injected intraperitoneally with 40 I.U. of L-asparaginase; the peak plasma activity after 4 hours was only 0.9 I.U. for the gel entrapped enzyme compared to a peak activity of 5.0 I.U. after 2 hours for the native L-asparaginase. Ninety percent of the plasma enzyme activity for the gel entrapped case was sedimentable at 21,000 X g, indicating a small leakage of the enzyme from the gel; the clearance for the enzyme activity in plasma had an initial half-life of 13 hours in contrast to a half-life of 2 hours for the native preparation. After intraperitineal injection of 5.0 I.U. into C3H mice, plasma L-asparagine fell to undetectable levels for 4 days and reappeared by day 8 for both the native and immobilized enzymes. Subcutaneously transplanted 6C3HED murine lymphoma was inhibited by 35, 78 and 100% after single intraperitoneal injections of immobilized L-asparaginase of 2, 4 and 8 I.U., respectively, as compared to 36, 53 and 86% for the native enzyme by the 14th day. Body weight changes after receiving immobilized L-asparaginase were essentially similar to those of animals receiving a comparable dose of native enzyme. These results indicate that while most of the immobilized L-asparaginase remains at the injection site, it produces a significant plasma L-asparagine depression and antitumor acitivity comparable to that of the native preparation without major toxicity.

Styrene and α-methylstyrene have been copolymerized at 60°C. At this temperature depropagation of the latter monomer must be considered. The rate of copolymerization and the chain length of the polymer formed are quantitatively interpreted by an extension of the theory previously used to describe the copolymer composition. It is postulated that rapid termination of copolymerization occurs because of the presence in the systems of low molecular weight free radicals of poly(α-methylstyrene) of chain length 3 cr less.