A Model of Closely Assembled Consecutive Enzymes on Membranes: Formation of Hydroxycinnamic Acids from L-Phenylalanine on Thylakoids ofDunaliella marina

Abstract

P-Hydroxycinnamic acid was found to be located within the plastids of the green alga Dunaliella marina. Thylakoid fractions desintegrated by ultrasonic treatment were capable of converting L-phenylalanine into o- and p-hydroxycinnamic acids; the hydroxylation reaction was increased by addition of NADPH. Hydroxycinnamic acids produced when [3-14C]cinnamate was incubated with varying amounts of [4'-3H]L-phenylalanine exhibited a 3H/14C ratio 10-150 times higher than that of the cinnamic acid reisolated from the incubation mixture. The lack of equilibration between cinnamate formed from L-phenylalanine and cinnamate added to the solution supports the hypothesis that cinnamate as an intermediate in hydroxycinnamate formation remains bound to the membrane enzyme complex. A model of membrane-bound multienzyme complexes is proposed for the conversion of aromatic amino acids into phenols.