木荷属和柃木属植物的嘌呤代谢及嘌呤碱合成研究

以［8-¹⁴C］标记的腺嘌呤和黄嘌呤为底物，对两种可以合成少量咖啡碱和茶叶碱的木荷属和柃木属植物（Schima mertensiana，Eurya japonica）叶片的嘌呤代谢进行了检测研究。发现木荷属和柃木属植物中嘌呤代谢相似，¹⁴C标记的腺嘌呤可以整合到嘌呤核苷酸、RNA、酰脲（包括尿囊素和尿囊酸）、二氧化碳中。经过24 h培养，在叶片吸收的放射能中，仅有6%～7%用于甲基黄嘌呤类化合物的合成（3-甲基黄嘌呤、7-甲基黄嘌呤核苷、7-甲基黄嘌呤、茶叶碱）。和其他植物一样，绝大多数¹⁴C标记的黄嘌呤整合到嘌呤的分解代谢物中（二氧化碳和酰脲），少量的放射能分布在3-甲基黄嘌呤及茶叶碱中。根据结果可以推断木荷属和柃木属植物具有N-甲基转移酶活性，可以用来合成咖啡碱和茶叶碱，相对于茶树而言，活性不高。综上，本文对木荷属和柃木属植物的嘌呤代谢以及嘌呤碱合成进行了研究。

Profiles of Purine Metabolism and Purine Alkaloid Biosynthesis in Schima and Eurya Plants

The metabolic fate of ［8-¹⁴C］ adenine and ［8-¹⁴C］ xanthine was examined in leaves of Schima mertensiana and Eurya japonica which produce small amounts of caffeine and theophylline. The profiles of purine metabolism in Schima and Eurya plants are similar. In both species, the radioactivity from ［8-¹⁴C］ adenine was incorporated into purine nucleotides, RNA, ureides (allantoin and allantoic acid) and CO₂. Only 6%-7% of the radioactivity taken up by the leaf disks was incorporated into methylxanthines (3-methylxanthine, 7-methylxantosine, 7-methyxanthine and theophylline) after 24 h incubation. Like other plant species, almost all radioactivity from ［8-¹⁴C］xanthine was incorporated into the purine catabolites (CO₂ and ureides), only small amounts of radioactivity were found in 3-methylxanthine and theophylline. We conclude that Schima and Eurya plants have N-methyltransferase activity for caffeine and theophylline biosynthesis, even though the activity is very low. The profiles of purine metabolism and purine alkaloid biosynthesis in Schima and Eurya plants were discussed.