NH2 CH COOH Figure 5-13 NH Ornithine COOH (P-OH,S CH3 HO H N-Methyl pyrrolinium Nicotinic acid mononucleotide (NADP+) COOH Nicotinic acid CHa Nicotine FIGURE 13.18 Nicotine biosynthesis begins with the biosyn thesis of the nicotinic acid (niacin) from aspartate and glyc- eraldehyde-3-phosphate. Nicotinic acid is also a component of NAD+ and NADP+, important participants in biological oxidation-reduction reactions. The five-membered ring of nicotine is derived from ornithine, an intermediate in argi nine biosvnthesisFigure 5-13