Abstract
This chapter discusses the biosynthesis and metabolism of caffeine and related purine alkaloids in plants. Caffeine and other purine alkaloids, including theobromine and theophylline, have played a major role in the long-standing popularity of non-alcoholic beverages and foods such as coffee, tea, cocoa, mate, chocolate and a wide range of soft drinks. This chapter begins by summarizing those aspects of general purine metabolism in plants that are related to purine alkaloid metabolism, and then provides an up-to-date account of the biosynthesis of caffeine and theobromine in a variety of plant species. Recent information on the properties and isolation of key enzymes, such as the caffeine synthase, are presented. Physiological studies on caffeine biosynthesis in tea and coffee plants including the authors' own work are also introduced. Catabolism of caffeine via demethylation to xanthine and degradation via the purine catabolism pathway in higher plants is then reviewed. The diversity of caffeine catabolism between species and between tissues of different age is considered. In young tea leaves, theophylline, a catabolite of caffeine, is reutilized for caffeine synthesis, but in aged Coffea arabica leaves 7-methylxanthine accumulates.