Phenolic metabolism in plants: intracellular localization of some enzymes

Two aspects of intracellular organization of phenol metabolism in plants were investigated. The first involved the localization of some reactions in the conversion of tyrosine to plastoquinone, which is accumulated in the chloroplast. More evidence is presented for the formation of p-hydroxyphenylpyruvic acid and homogentisic acid from tyrosine by higher plants, although neither reaction seems to occur in the chloroplast. The second part of this work involved the intracellular localization of several enzymes involved in the phenolic metabolism of potato. Separation of cell fractions by differential centrifugation and sucrose density gradient separation showed that shikimate dehydrogenase and prephenate dehydrogenase are wholly soluble enzymes. In the cases of phenylalanine ammonia lyase and an 0-methyl transferase acting on caffeic acid, 90% of the enzyme was soluble. The remaining 10% of the enzymes that was associated with particulate fractions did not appear to be located in the same fractions. Most of the cinnamic acid hydroxylase in aged potato was found in the microsomal fraction, but some of this enzyme appeared to be associated with other particles. All the enzymes studied increased two-fold or more in activity after the potato tuber was sliced and aged in the light. Cinnamic acid hydroxylase increased in activity and also changed from a mainly soluble enzyme in dormant potato to the microsomal enzyme characteristic of actively metabolizing tissue.Science, Faculty ofBotany, Department ofGraduat