Incorporation of glyceraldehyde into the pyridine ring of nicotine.

D-Glyceraldehyde-3J4C was synthesized and administered to intact Nicotiana rustica. Degradation of the pyridine moiety of nicotine produced by these plants showed that over half of the incorporated 1% was in position 4 of the pyridine ring, and the remainder of the radioactivity was divided almost equally among carbon atoms 2, 3, and 6. Lack of randomization of the label in positions 4, 5, and 6 indicates that a nonsymmetrical compound condenses with aspartate to form the pyridine ring. Glyceraldehyde-3J4C was incorporated into the pyridine ring with a dilution of about 217 as compared with a dilution of about 300 when 14C-labeled glycerol was used as the precursor. This finding suggests that D-glyceraldehyde may be a more immediate precursor of the pyridine ring than glycerol. Incorporation of 14C into carbon atoms 2 and 3 of the pyridine ring indicates that D-glyceraldehyde is phosphorylated and metabolized through glycolysis to form acetate-z14C which is then converted to aspartate-2 ,3J4C through the reactions of the tricarboxylic acid cycle.