In enzymology, a theobromine synthase (EC 2.1.1.159) is an enzyme that catalyzes the chemical reaction

S-adenosyl-L-methionine + 7-methylxanthine ${\displaystyle \rightleftharpoons }$ S-adenosyl-L-homocysteine + 3,7-dimethylxanthine

Thus, the two substrates of this enzyme are S-adenosyl methionine and 7-methylxanthine, whereas its two products are S-adenosylhomocysteine and 3,7-dimethylxanthine.

This enzyme belongs to the family of transferases, specifically those transferring one-carbon group methyltransferases. The systematic name of this enzyme class is S-adenosyl-L-methionine:7-methylxanthine N3-methyltransferase. Other names in common use include monomethylxanthine methyltransferase, MXMT, CTS1, CTS2, and S-adenosyl-L-methionine:7-methylxanthine 3-N-methyltransferase.

References

• Ogawa M, Herai Y, Koizumi N, Kusano T, Sano H (2001). "7-Methylxanthine methyltransferase of coffee plants. Gene isolation and enzymatic properties". J. Biol. Chem. 276 (11): 8213–8. doi:10.1074/jbc.M009480200. PMID 11108716.
• Uefuji H, Ogita S, Yamaguchi Y, Koizumi N, Sano H (2003). "Molecular cloning and functional characterization of three distinct N-methyltransferases involved in the caffeine biosynthetic pathway in coffee plants". Plant Physiol. 132 (1): 372–80. doi:10.1104/pp.102.019679. PMC 166982. PMID 12746542.
• Yoneyama N, Morimoto H, Ye CX, Ashihara H, Mizuno K, Kato M (2006). "Substrate specificity of N-methyltransferase involved in purine alkaloids synthesis is dependent upon one amino acid residue of the enzyme". Mol. Genet. Genomics. 275 (2): 125–35. doi:10.1007/s00438-005-0070-z. PMID 16333668. S2CID 8338121.