<prompt> Endogenous production of Niacin is fromTyrosineThreonineTryptophanAlanine  <response>: Ans. c Tryptophan Ref. Harpers Biochemistry 27th ed. 498 Niacin is synthesized from Tryptophan. 60 mg of Tryptophan gives 1 mg equivalent of niacin. Active forms of Niacin, are NAD and NADP.Educational points:AMINO ACID DERIVATIVES Ornithine -Putrescine - Spermidine -Spermine Polyamine biosynthesis - One of the earliest signals that cells have entered their replication cycle is the appearance of elevated levels of mRNA for ornithine decarboxylase ODC, and then increased levels of the enzyme, which is the first enzyme in the pathway to synthesis of the polyamines. Arginine -Citrulline NO 