The effects of sunflower l-phenylalanine ammonia-lyase inactivating factor on Rhodotorula glutinis l-phenylalanine ammonia-lyase

Abstract Phenylalanine ammonia-lyase inactivating factor (IF) prepared from chloroplasts isolated from sunflower leaves was utilized to study its inactivating effects on l -phenylalanine ammonia-lyase from Rhodotorula glutinis in vitro . The effects of inactivation by inactivating factor were compared with those caused by chemicals such as sodium borohydride and nitromethane. The sunflower inactivator acted as an enzyme and enzymatic inactivation caused irreversible loss of phenylalanine ammonia-lyase catalytic activity accompanied by shortening of the enzyme molecule. However, the capacity of IF-inactivated phenylalanine ammonia-lyase to bind to l -phenylalanine, the enzyme substrate, was maintained. These effects of the inactivating factor from sunflower leaves are quite different from those of inhibitors (reversible loss of catalytic activity) isolated from different sources by other workers. The results suggest that inactivation plays an important role in in vivo regulation of phenylpropanoid metabolism.