Induction of Phenylalanine Deaminase by Light and its Relation to Chlorogenic Acid Synthesis in Potato Tuber Tissue

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Abstract
Fresh potato tuber tissue had no phenylalanine deaminase activity. Enzyme activity was readily demonstrated in extracts of tuber disks maintained in a moistened condition for 16-24 hours previous to extraction. The appearance of enzyme activity was stimulated greatly by exposure of the tissue to white light during culture, a condition which stimulated protein synthesis in the tissue. Ethionine and analogues of purines and pyrimidines inhibited the appearance of enzyme activity. It is suggested that an actual synthesis of enzyme molecules occurred during the period of culture, and that the appearance of activity represented an induction of enzyme synthesis in the tissue. Evidence is presented for the repression of synthesis of the deaminase by the product of its reaction, cinnamic acid. The initial rate of chlorogenic acid synthesis from endogenous substrates was directly proportional to the activity of the enzyme in the disks. Under these conditions of culture, the regulation of phenolic synthesis by light occurred at the enzyme level.