Biosynthese von p-Hydroxybenzoesäure und anderer Benzoesäuren in höheren Pflanzen

Abstract

Feeding experiments with glucose- (2-¹⁴C), phenylalanine- (3-¹⁴C), tyrosine- (3-¹⁴C) and p-coumaric acid- (3-¹⁴C) showed that the latter three substances are incorporated in good yields into p-hydroxybenzoic acid in leaves of Catalpa ovata. Kinetic experiments showed that p-hydroxybenzoic acid is formed from phenylalanine via p-coumaric acid and the subsequent β-oxidation of the side chain. p-Hydroxybenzoic acid can also be synthetised by hydroxylation of benzoic acid, but this does not seem to be the biosynthetic route in Catalpa. Phenylalanine- (3-¹⁴C) is also incorporated into benzoic acid, protocatechuic acid, and vanillic acid by different plants; the radioactivity of the β-C atom of the amino acid was found in each case to be located in the carboxyl group of the C₆ — C₁ acid. This suggests that in higher plants the benzoic acids are formed from the corresponding cinnamic acids via β-oxidation.