The main ways to synthesize NAD+ The synthesis of NAD+ is divided into salvage pathway, de novo synthesis pathway and Preiss-handler pathway according to different synthetic raw materials. a) De novo synthesis pathway: tryptophan (Trp) is converted to quinolinic acid (QA), and then converted to NAMN by quinolinic acid-phosphoribosyl transferase (QPRT). NAMN is converted into NAAD, and finally NAD+ is …