The preparation and activity of a phenylanine ammonia-lyase inactivator from sunflower leaves

Isolated plastids from crude extracts of sunflower ( Helianthus annuus L. cv. Sungold) leaves released a factor on extraction with Triton X-100 that inactivated Rhodotorula glutinis L-phenylaine ammonia-lyase (PAL; EC 4.3.1.5) in vitro. This PAL-inactivating factor (PAL-IF) was found to be proteinaceous in nature when tested with pronase (EC 1.11.1.6), peroxidase (EC 1.11.1.7) and nitrate reductase and the protection of PAL from PAL-IF by ligands indicated its specificity towards PAL. The inactivated PAL inhibitors reported earlier. It is suggested that inactivation may play an important role in in vivo regulation of L-phenylalanine ammonia-lyase activity and phenolic biosynthesis.