BIOSYNTHESIS 



31. C. J. Watson and J. A. Layne, ibid., 200. 



32. C. Rimington and Z. A. Leitner, Lancet, 1945, 2, 494. 



33. V. P. Sydenstricker, Ann. intern. Med., 1941. 14, 1499. 



34. W. H. Sebrell and R. E. Butler, U.S. Publ. Health Rep., 1938, 53, 



2282. 



35. T. Gillman and J. Gillman, Arch, intern. Med., 1945, 76, 63. 



36. F. Mainzer and M. Krause, Brit. Med. J., 1939, 2, 331. 



37. N. JollifEe, K. M. Bowman, L. A. Rosenblum and H. D. Fein, 



/. Amer. Med. Assoc, 1940, 114, 307. 



38. R. M. Cleckley, V. P. Sydenstricker and L. E. Geeslin, ibid., 1939, 



112, 2107. 



39. J. D. King, Lancet, 1940, 2, 32; Brit. Dental J., 1943, 74, 113, 



141, 169. 



40. V. P. Sydenstricker and R. M. Cleckley, Amer. J, Psychiat., 1941, 



98. 83. 



41. F. J. Neuwahl, Lancet, 1942, 2, 419. 



42. G. Melton, Brit. Med. /., 1943, 1, 600. 



43. M. Atkinson, Arch. Otolaryngol., 1944, 40, loi. 



44. L. A. Crandall, F. F. Chesley, D. Hansen and J. Dunbar, Proc. 



Soc. Exp. Biol. Med., 1939, 41, 472. 

 45- J- W. Graham, /. Amer. Med. Assoc, 1939, 113, 664. 

 46. W. W. Kiihnau, Klin. Woch., 1939, 18, 11 17. 



9. BIOSYNTHESIS OF NICOTINIC ACID 



Two contrasting views have been advanced to account for the 

 interchangeability of nicotinic acid and tryptophan. It is main- 

 tained on the one hand that trjrptophan is directly converted into 

 nicotinic acid in the tissues of animals, and on the other that trypto- 

 phan acts as a catalyst for the synthesis of nicotinamide by intestinal 

 bacteria. 



The evidence supporting the first hypothesis is as follows. Symp- 

 toms of nicotinic acid deficiency in the pig,^ the dog,^ and in humans ^ 

 were relieved by the administration of L- tryptophan, and the reserves 

 of nicotinic acid and the urinary excretion of nicotinic acid meta- 

 bolites were thereby increased. Administration of sulphasuxidine 

 did not impair the action of tryptophan in relieving symptoms of 

 pellagra in humans, although such a result could be anticipated if 

 the intestinal flora were involved. Moreover, the intravenous ad- 

 ministration of L-tryptophan to infants gave a prompt and large 

 increase in the urinary output of N^-methylnicotin amide.* The 

 synthesis of nicotinic acid by rats was apparently not affected by 

 elimination of the bacterial flora ^ or by enterectomy ; ^ and nicotinic 

 acid was synthesised from tryptophan by rat liver slices. '^ Indirect 

 evidence in support of the view that tryptophan is converted directly 

 into nicotinic acid is that the presence of pyridoxine is essential for 



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