Metabolism of purine alkaloids and xanthine in leaves of maté (Ilex paraguariensis)

Abstract

Accumulation and metabolism of purine alkaloids in leaves of maté (Ilex paraguariensis) were investigated. In winter, leaves accumulated caffeine but not theobromine, indicating that caffeine is the end product of purine alkaloid synthesis in maté. To elucidate the purine alkaloid metabolism in maté leaves, the metabolic fate of [8-(14)C]theobromine, [8-(14)C]theophylline, [8-(14)C]caffeine and [8-(14)C] xanthine was investigated in the leaf disks of young and mature leaves. In young maté leaves, significant amounts of theobromine and theophylline were utilized for caffeine biosynthesis, but the conversion was not observed in mature leaves. A small amount of theophylline was converted to theobromine. Practically no caffeine catabolism was detected in maté leaves during a 24 h-incubation. Catabolism of theobromine and theophylline via 3-methylxanthine was observed mainly in mature leaves. Xanthine was catabolised extensively via ureides in both young and mature leaves, but limited amounts are also utilized for the synthesis of theobromine, theophylline and caffeine. Possible pathways for the metabolism of purine alkaloids in maté leaves are discussed.