Purine alkaloid metabolic pathway. Dotted line indicates that some metabolites have been omitted. The column chart shown that the gene expression of three tea samples. The red genes play a synthetic role and the blue represent degradation. *SAMS, S-adenosylmethionine synthetase, APRT, adenine phosphoribosyltransferase; NK, nucleoside kinase; 5′-NT, 5′-nucleotidase; 3-NMT and 1-NMT, tea caffeine synthase (TCS); N-MeNase, N-methyl nucleosidase; CYP1A2, cytochrome P450 family 1 subfamily apolypeptide 2; ALN, allantoinase; URE, urease.