Involved in the biosynthesis of pyridine alkaloid natural products, leading mainly to the production of anabasine, anatabine, nicotine and nornicotine, effective deterrents against herbivores with antiparasitic and pesticide properties (neurotoxins); nornicotine serves as the precursor in the synthesis of the carcinogen compound N'-nitrosonornicotine (NNN) (PubMed:32242247). Catalyzes the oxidation of L-aspartate to iminoaspartate (By similarity). L-aspartate + O2 = H2O2 + iminosuccinate Binds 1 FAD per subunit. Alkaloid biosynthesis; nicotine biosynthesis. Cofactor biosynthesis; NAD(+) biosynthesis; iminoaspartate from L-aspartate (oxidase route): step 1/1. Reduced alkaloids and nicotin levels associated with a lower putrescine production (PubMed:32242247). Occasionally, an early senescence and a lower viability of the older leaves is observed (PubMed:32242247). Belongs to the FAD-dependent oxidoreductase 2 family. NadB subfamily.