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Incorporation of Aspartate and Malate into the Pyridine Ring of Nicotine

From the ¹ From the Department of Biochemistry, Michigan State University, East Lansing, Michigan

A unique nicotinic acid degradation was devised which permitted the isolation of each individual carbon atom of the pyridine ring.

Aspartate-3-¹⁴C and malate-3-¹⁴C were administered to Nicotiana rustica tobacco plants for 4 hours and found to be incorporated almost exclusively into carbons 2 and 3 of the pyridine ring of nicotine. When aspartate-3-¹⁴C was fed, 57% of the tracer resided at carbon 3 and 38% at carbon 2. Malate-3-¹⁴C labeled carbon 3 with 61% of the isotope and carbon 2 with 38%. The dilution of incorporation of aspartate-3-¹⁴C was 600 and of malate-3-¹⁴C, 1260.

The incorporation of aspartate and malate with low dilution and the lack of randomization of ¹⁴C between carbons 2 and 3 of the pyridine ring indicate either that aspartate or malate is the immediate precursor of the pyridine ring of nicotine, or that they are converted to the immediate precursor without passing through a symmetrical intermediate.

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