Pan Si-An, Sun Ying, Li Mengmeng, Deng Wei-Wei, Zhang Zheng-Zhu
State Key Laboratory of Tea Plant Biology and Utilization, Anhui Agricultural University 130 Changjiang West Road Hefei Anhui 230036 China
RSC Adv. 2019 Nov 7;9(62):36136-36143. doi: 10.1039/c9ra05655f. eCollection 2019 Nov 4.
Wet piling is a key process for producing pu'erh tea because various components change under the action of microorganisms. Among these components, caffeine content is increased. Evidence has indicated a salvage pathway for caffeine biosynthesis in microbes, in which xanthine is methylated in the order of N-3 → N-1 → N-7. In addition, guanine can be used to synthesize xanthine through guanine deaminase (EC: 3.5.4.3). In this study, we investigated the variation in caffeine content during piling fermentation with supplementary guanine, N-labeled guanine and xanthine. We cloned the guanine deaminase gene () from (one dominant strain in piling fermentation). The results revealed that [N]xanthine could be synthesized from [N]guanine, and [N]caffeine was also detected during piling with supplementary [N]xanthine. Furthermore, ScGUD1 could catalyze the conversion of guanine to xanthine, which is likely to be methylated for caffeine synthesis under microorganism action. The obtained results revealed the mechanism underlying the increased caffeine content during piling of pu'erh tea.
渥堆是生产普洱茶的关键工序，因为在微生物作用下各种成分会发生变化。在这些成分中，咖啡因含量会增加。有证据表明微生物中存在咖啡因生物合成的补救途径，其中黄嘌呤按N-3→N-1→N-7的顺序甲基化。此外，鸟嘌呤可通过鸟嘌呤脱氨酶（EC：3.5.4.3）用于合成黄嘌呤。在本研究中，我们用补充鸟嘌呤、N标记的鸟嘌呤和黄嘌呤研究了渥堆发酵过程中咖啡因含量的变化。我们从（渥堆发酵中的一种优势菌株）克隆了鸟嘌呤脱氨酶基因（）。结果表明，[N]黄嘌呤可由[N]鸟嘌呤合成，在补充[N]黄嘌呤的渥堆过程中也检测到了[N]咖啡因。此外，ScGUD1可催化鸟嘌呤转化为黄嘌呤，在微生物作用下黄嘌呤可能会甲基化用于咖啡因合成。所得结果揭示了普洱茶渥堆过程中咖啡因含量增加的机制。
