Chlorogenic acid biosynthesis : Incorporation of [α- 14C]cinnamic acid into the cinnamoyl and hydroxycinnamoyl conjugates of the potato tuber

Abstract

Experiments in which potato tuber slices were maintained on a tracer amount of [α- 14C]cinnamic acid and synthetic 3- 0-cinnamoylquinic acid (pH adjusted to 6) showed that if this conjugate is a free intermediate in chlorogenic acid (3- 0-caffeoylquinic acid) formation, then the active pool of the compound is very small and is contained within a cell compartment whose membrane is relatively permeable to phenylalanine and cinnamic acid but not to the conjugate itself. The specific activities of 3- 0-cinnamoyl-, 3- 0- p-coumaroyl-, and 3- 0-caffeoylquinic acid; 3- 0- p-coumaroyl-, and 3- 0-caffeoylshikimic acid; and 1- O- p-coumaroyl-, and 1- O-caffeoyl-β- d-glucose were determined in this experiment. The results of similar experiments on which tuber slices were maintained on [α- 14C]cinnamic acid and quinic acid, or phenylalanine and quinic acid together with a tracer amount of [α- 14C]cinnamic acid, are reported. The specific activities of the isolated conjugates indicate that in each series the caffeoyl derivatives are formed by the hydroxylation of the p-coumaroyl derivatives. The specific activity data also suggest that cinnamic acid and the derived conjugates are formed within a compartment or compartments of the cell.