Phenylalanine ammonia lyase-inactivating system in sunflower leaves

Abstract A high MW fraction extracted from sunflower leaves inactivates the phenylalanine ammonia-lyase (PAL) from sunflower and Rhodotorula glutinus . The pH optimum for inactivation was 9·5. The K m of the phenylalanine ammonia-lyase-inactivating system (PAL-IS) was estimated to be 35 mU PAL/ml. D-phenylalanine was an effective inhibitor of inactivation. Fresh tissue had a low level of PAL-IS, but the level increased upon sucrose treatment with light and was maintained during subsequent treatment of leaves in darkness on water.