Phytochrome-mediated de novo synthesis of phenylalanine ammonia-lyase: An approach using pre-induced mustard seedlings.

The molecular mechanism of enzyme (phenylalanine ammonia-lyase; EC 4.3.1.5) formation mediated by phytochrome in mustard seedlings was investigated by labeling the enzyme with deuterium followed by high resolution CsCl density gradient analysis. A favorable relationship between induced rise of activity and turnover of this short-lived enzyme (half-life 3-4 hr) was achieved by labeling pre-irradiated seedlings. The time course of deuterium incorporation during the light-mediated rise in enzyme activity that can be derived independently from density shifts and bandwidth changes demonstrates a stimulation of synthesis and degradation by phytochrome. When synthesis is faster than degradation, enzyme accumulates.