Caffeine demethylase

N-demethylase activity was monitored by the CBT, and 7-N-demethylase activity was monitored by the caffeine urinary metabolite ratio (CMR). PBB-exposed subjects had higher CBT values (p<0.02) than urban nonsmokers, but tire values were comparable to those of urban smokers. The correlation between serum PBB levels and the CBT value was poor (r ().2). The CMR value in PBB-exposed subjects was also higher than that of urban nonsmokers (p<0.05) there was no correlation between serum PBB levels and CMR values. Generally, smokers have higher CBT values than nonsmokers due to the presence of polycyclic aromatic hydrocarbons (PAH) in tobacco smoke, which induce CYPIA (Kotake et al. 1982). 

Fig. 293 3-Methylxanthme, 1-methylxanthine, and theophylline are synthesized fiom caffeine as part of the caffeine degradation pathway that produces xanthine which is further degraded to CO2 and NH3 by the craivcaitional oxidative piuine catabolism pathway. The conversion of caffeine to theophylline is the rate-limiting step in caffeine-accumulating species such as Coffea arabica and Camellia sinensis. Solid arrows indicate major routes and dotted arrow minor conversions. The pathway was elucidated from data obtained in feeding experiments. Y-Demethylase enzymes involved in caffeine degradation have not yet been characterized in plants. Enzymes NDM iV-demethylase, XDH xanthine dehydrogenase...

Fig. 29.4 Proposed biosynthesis of liberine from caffeine [26], Enzymes COD caffeine oxidase, OMT 0-methyltransferase, WDM W-demethylase...

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