Caffeine, biosynthesis

Several studies have investigated the biosynthesis of caffeine in tea. The results of a study by Suzuki and Takahashi27 30 suggest a pathway for caffeine biosynthesis in tea from 7-methylxanthine to theobromine and then to caffeine. Additionally they suggest that theophylline is synthesized from 1-methylxanthine. Another study by Ogutuga and Northcote31 proposes a pathway through 7-methylxanthosine to theobromine followed by caffeine. 

While caffeine biosynthesis in coffee and tea has been reasonably well investigated, little information is available about the biosynthetic pathways of methylxanthines in cacao. Published studies34 35 have established the presence of 7-methylxanthine and adenine in cocoa. Since both coffee and tea exhibit similar pathways where theobromine is a direct precursor for caffeine, it is reasonable to assume that a similar mechanism is possible in cacao. 

Schulthess, B.H. and Baumann, T.W., Stimulation of caffeine biosynthesis in suspension cultured coffee cells and the in-situ existence of 7-methylxanthosine, Phytochemistry, 38,1381,1995. 

Suzuki, T. and Takahashi, E., Caffeine biosynthesis in Camellia sinensis, Phytochemistry, 15,1235,1976b. 

Ogita, S, Uefuji, H Morimoto, M. and Sano, H. 2004. Application of RNAi to confirm theobromine as the major intermediate for caffeine biosynthesis in coffee plants with potential for construction of decaffeinated varieties. Plant Molecular Biology, 54(6) 931-941. 

The PA caffeine is produced from xanthosine via three distinct N-methylations (Fig.7.5).87 89 Partially purified enzyme extracts from tea (Camellia senensis) and coffee (Coffea arabica) were shown to exhibit all three activities, suggesting either that the A-methyltransferase steps in caffeine biosynthesis are catalyzed by a single enzyme, or by multiple enzymes with similar properties.90 However, a specific A-methyltransferase purified from coffee was active only toward 7-methylxanthine and theobromine91 An A-methyltransferase catalyzing the methylation of methylxanthines and designated caffeine synthase (CS) was purified from tea.92 CS catalyzes two consecutive methylations involved in the conversion of 7-methylxanthine to caffeine, but is inactive toward xanthosine, indicating that the first methylation proceeds via a different enzyme. Heterologous expression of the CS cDNA showed that the enzyme was active toward 7-methylxanthine, paraxanthine,... 

KATO, M., KANEHARA, T., SHIMIZU, H SUZUKI, T GILLIES, F.M., CROZIER, A., ASHIHARA, H., Caffeine biosynthesis In young leaves of Camellia sinensis in vitro studies on TV-methyltransferase activity involved in the conversion of xanthosine to caffeine. Physiol. Plant, 1996,98,629-636. 

WALDHAUSER, S. S. M KRETSCHMAR, J. A., BAUMANN, T. W N-methyltransferase activities in caffeine biosynthesis Biochemical characterization and time course during leaf development of Coffea arabica., Phytochemistry., 1997, 44, 853-859. 

Caffeine, a purine alkaloid, is one of the most widely known natural products. Caffeine is ingested as a natural component of coffee, tea, and cocoa, and the impact of caffeine on human health has been studied extensively. The biosynthetic pathway of caffeine has been elucidated recently on the genetic level. Caffeine biosynthesis has been studied most widely in the plant species Coffea (coffee) and Camellia (tea) (168, 169). 

Xanthosine, which is derived from purine metabolites, is the first committed intermediate in caffeine biosynthesis (Fig. 4). Xanthosine can be formed from de novo purine biosynthesis, S-adenosylmethione (SAM) cofactor, the adenylate pool, and the guanylate pool (169). De novo purine biosynthesis and the... 

Figure 4 Caffeine biosynthesis. XMT, xanthosine N-methyltransferase (also called 7-methylxanthosine synthase) XN, methyixanthosine nucleotidase MXMT, 7-methylxanthine-N-methyltransferase (also called theobromine synthase) DXMT, dimethyIxanthine-N-methyltransferase (also called caffeine synthase).

Mizuno K, Kato M, Irino F, Yoneyama N, Fujimura T, Ashihara H. The first committed step reaction of caffeine biosynthesis 7-methylxanthosine synthase is closely homologous to caffeine synthase in coffee. FEES Lett. 2003 547 56-60. 

Waldhauser SSM, Gillies FM, Crozier A, Baumann TW. Separation of the N-methyltransferase the key enzyme in caffeine biosynthesis. Phytochemistry 1997 45 1407-1414. 

Ashira H, Zheng XQ, Katahira R, Morimoto M, Ogita S, Sano H. Caffeine biosynthesis and adenine metabohsm in transgenic Coffea canephora plants with reduced expression of N-methyltransferase genes. Phytochemistry 2006 67 882-886. 

Satyanarayana KV, Kumar V, Chandrasheker A, Ravishankar GA. Isolation of promoter for N-methyltransferase gene associated with caffeine biosynthesis in Coffea canephora. J. Biotech-nol. 2005 119 20-25. 

Various minor routes, dependent upon the broad specificities of the fV-methyltransferases, may also operate in addition to the main caffeine biosynthesis pathway. For instance, caffeine synthase catalyzes the biosynthesis of 3-methylxanthine from xanthine. Paraxanthine is biosynthesized from 7-methylxanthine. 3-Methylxanthine and paraxanthine are immediately converted into caffeine. Paraxanthine is the most active substrate of caffeine synthase, but only limited amounts of paraxanthine accumulate in plant tissues because the N-1 methylation of 7-methylxanthine is very slow [259, 260]. 

Table 29.1 Genes of iV-methyltransferases involved in caffeine biosynthesis isolated from coffee (Coffea arabica) plants...

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