Abstract [6-14 C, 2-3 H] Nicotinic acid,[6-14 C, 6-3 H] nicotinic acid,[methyl-14 C, 2-2 H, 3 H] trigonelline, and [methyl-14 C, 6-2 H, 3 H] trigonelline were all incorporated into the isoquinuclidine moiety of the alkaloid dioscorine found in the yam Dioscorea hispida with complete retention of 3 H relative to 14 C. A chemical degradation] on the dioscorine derived from the labelled trigonellines indicated that all the 14 C was located on its N-methyl ...