IV. BIOCHEMICAL SYSTEMS 505 



listed below may exist, but at least these reactions make possible one route 

 of formation. 



1. Synthesis of Nicotinic Acid 



The sources of nicotinic acid may be diet, the conversion of tryptophan 

 to nicotinic acid (p. 523), or possibly intestinal microorganisms (p. 530). 



2. Amidation of Nicotinic Acid 



Ellinger^^^ has shown that kidney and Ijrain slices are capable of amidating 

 nicotinic acid. Liver sHces can also accomplish this conversion if a source 

 of NHs such as glutamine is provided. Slices from several other tissues were 

 unable to accomplish this conversion. It was assumed from early studies 

 that erythrocytes (human) could also amidate nicotinic acid since, both 

 in vivo and in vitro, nicotinic acid but not nicotinamide produced an increase 

 within the erythrocytes of material which had activity for Hemophilus 

 parainfluenza, for Hemophilus influenza, or for DPN-linked enzyme sys- 

 tems. ^^^-^^^ Furthermore, Liefer et al}^^ used carboxyl-C"-labeled nicotinic 

 acid and nicotinamide to show a rapid uptake and fixation of nicotinic 

 acid within the erythrocyte (mice). Nicotinamide, on the other hand, was 

 taken up by the erythrocytes but could be washed out readily, indicating 

 that it had not been incorporated into fixed non-diffusible molecules. 



More recently, Leder and Handler^^ have found just the contrary, i.e., 

 that nicotinamide but not nicotinic acid resulted in an increased synthesis 

 of coenzyme-active material in erythrocytes. A good explanation for these 

 contradictory results is not apparent. 



3. Synthesis of Ribose 



A mechanism which can account for the synthesis of ribose from glucose 

 has already been detailed (p. 500). Other mechanisms are possible.'*^ 



4. Synthesis of Nicotinamide Mononucleotide 



This fragment of the molecule (nicotinamide-ribose-phosphate) can be 

 synthesized by erythrocytes incubated with nicotinamide and glucose.^^ A 



" P. Ellinger, Biochem. J. 42, 175 (1948). 



« H. I. Kohn and J. R. Klein, J. Biol. Chem. 130, 1 (1939). 



^9 H. I. Kohn and J. R. Klein, /. Biol. Chem. 135, 685 (1940). 



5" C. L. Hoagland and S. M. Ward, /. Biol. Chem. 146, 115 (1942). 



" P. Handler and H. I. Kohn, J. Biol. Chem. 150, 447 (1943). 



52 C. L. Hoagland, S. M. Ward, and R. E. Shank, /. Biol. Chem. 151, 369 (1943). 



" E. Leifer, J. R. Hogness, L. J. Roth, and W. H. Langham. /. Am. Chem. iSoc. 70, 



2908 (1948). 

 " B. L. Horecker, in Phosphorus Metabolism, Chapter III. The Johns Hopkins 



Press, Baltimore, 1951. 



