VI. BIOGENESIS 531 



found monomethyltryptophan (presumably amino-N-methyltryptophan) 

 equally effective by mouth or parenterally in increasing the urinary excre- 

 tion of nicotinamide and its derivatives in rats. 



3. Utilization of l- and d-Tryptophan as Precursors for 

 Nicotinic Acid 



a. In Rat 



There is a very limited amount of information on this subject. Both d- 

 and L-tryptophan can be used by the rat for nicotinic acid synthesis, al- 

 though D-tryptophan is somewhat less efficiently utilized.^'' **• ''-■ ^^ Acetyl- 

 D-tryptophan, however, was completely inactive, and acetyl-L-tryptophan 

 was only about one-half as active as L-tryptophan. ''^ 



6. In Poultry 



In the chick, Grau and Almquist^"" found D-tryptophan to be completely 

 inactive, although later studies by Wilkening and Schweigert^"^ indicated 

 that the chick could use D-tryptophan 17 to 40% as efficiently as L-tryp- 

 tophan. Kratzer et aZ.^"^ found D-tryptophan to be 30 % as active as L-tryp- 

 tophan in turkey poults. These studies in poultry evaluated the utilization 

 of D-tryptophan for growth. Its effect on nicotinic acid requirements was 

 not studied. Utilization of the isomers would not necessarily be the same 

 in the conversion of tryptophan to nicotinic acid. Anderson et aZ.'"^ studied 

 this question in chicks under conditions where they could measure the 

 nicotinic acid-replacing value of the isomers of tryptophan. These workers 

 could find no evidence that D-tryptophan was utilized as a precursor of 

 nicotinic acid when the diet contained glucose as the principal carbohydrate. 

 However, when the ration contained starch, D-tryptophan was utilized to a 

 limited extent. These facts, plus the finding that the utilization of D-tryp- 

 tophan was reduced when the starch ration contained sulfasuxidine, indi- 

 cate that intestinal microorganisms may play some role in the utilization 

 of D-tryptophan. 



c. In Dogs 



In dogs, Singal and associates'^ obtained evidence that only L-tryptophan 

 was used as a precursor for nicotinic acid in spite of the fact that DL-tryp- 



99 W. A. Krehl, P. S. Sarma, L. J. Teply, and C. A. Elvehjem, /. Nutrition 31, 85 



(1946). 

 100 C. R. Grau and H. J. Almquist, /. Nutrition 28, 263 (1944). 

 >oi M. C. Wilkening and B. S. Schweigert, ./. Biol. Chem. 171, 209 (1947). 

 '02 F. H. Kratzer, D. E. Williams, and B. Marshall, J. Nutrition 43, 223 (1951). 

 •03 J. O. Anderson, G. F. Combs, and G. M. Briggs, /. Nutrition 42, 463 (1950). 



