Uncoupling Effect of Hydroxycinnamic Acid Derivatives on Pea Chloroplasts

Abstract

Summary The effect of p-coumaric acids as well as the glucoside of caffeic acid at concentrations of 10-7 to 10-4 M on ferricyanide photoreduction, ATP synthesis and proton exchange parameters in pea chloroplasts has been studied. All the 3 compounds were shown to activate electron transport and to inhibit hotophosphorylation. Caffeic acid has the greatest effect, since it inhibits proton uptake by 40% at 10-4 M, whereas the dissipation constant of proton gradient has the greatest value under the effect of pcoumaric acid (140% at 10-4 M). The protolytic properties of the substances under study have been determined by the buffer capacity method. The ρssssK values of p-coumaric acid (4.8 and 9.15), caffeic acid (4.9; 8.85 and > 10) and caffeic acid glucoside (8.6 and > 10) were obtained. It is suggested that the uncoupling effect of hydroxycinnamic acids is due to their acid-base properties and the ability to form complexes with divalent metal ions.