Purine Degradative Pathway of the Yam and Sweet Potato

The degradation of purines by nitrogen-deficient plants was investigated in the carbohydrate staples yam tubers (Dioscorea spp.) and sweet potatoes (Ipomoea batatas). The activities of adenosine deaminase, xanthine oxidase, uricase, allantoinase, allantoicase, and allantoate amidohydrolase were detected in extracts of the tubers, showing that purine degradation operates in these nitrogen-deficient plants as in the case of nitrogen-rich plants. The presence of allantoate amidohydrolase in the tubers suggested that much ammonia was lost from the pathway. Stored tubers also had increased activities of some enzymes of the pathway and experienced high losses of nitrogen. These results indicate that the nitrogen deficiency of root tubers was in part attributed to the ammonia lost via the purine degradative pathway. The implications of these reactions are discussed as they affect storage of the tubers for food uses. © 1986, American Chemical Society. All rights reserved