ylalanine ammonia-lyase after a single injection, L5178Y munine lymphoblastic leukemia and 15091A anaplastic can cinoma significantly depressed the maximal level of phenyl alanine ammonia-lyase attained in the plasma. After repeated injections of phenylalanine ammonia

Yeast phenylalanine ammonia-lyase was administered i.p. to normal and tumor-beaning mice, and its clearance from plasma was studied. Single and multiple weekly injections at dosages of 10, 20, 50, and 100 units/kg were adminis tered to C57BL female, C57BL x DBA/2 F male, and A/J female mice. L5178Y munine lymphoblastic leukemia, B16 melanoma, BW10232 adenocancinoma, and 15091A ana plastic carcinoma were implanted 7 to 11 days prior to enzyme injection in the appropriate host. After a single injection, the average plasma half-lives of phenylalanine ammonia-lyase were 18 to 24 hr in all groups studied. While the other tumors had no effect on the plasma level of phen ylalanine ammonia-lyase after a single injection, L5178Y munine lymphoblastic leukemia and 15091A anaplastic can cinoma significantly depressed the maximal level of phenyl alanine ammonia-lyase attained in the plasma. After repeated injections of phenylalanine ammonia lyase, the initial plasma enzyme level was significantly re duced when 20 units/kg were administered, and the clean ance of the enzyme from the plasma was greatly accelerated regardless of the amount administered. Furthermore, in tumor-beaning mice, the rate of clearance was significantly more rapid than in the appropriate non-tumor-beaning con tnol.