286 THE BIOCHEMISTRY OF B VITAMINS 



it cannot be used. In the previously mentioned work of Polonovski et al. 107 

 it was found that certain pterins could substitute for riboflavin in pigeons 

 and rats. Ten jxg per day of fluorescyanine produced a growth rate in 

 riboflavin deficient rats of 2 gm/day, similar to that produced by ribo- 

 flavin. A large variety of synthetic riboflavin derivatives have been pre- 

 pared, and much has been learned in this manner regarding the structural 

 specificity associated with the riboflavin molecule, but these substances 

 per se are of little interest in the present discussion. 



(3) Nicotinic Acid 



There are probably more known nutritionally active substances isotelic 

 with nicotinic acid than with any of the other B vitamins. Many of these 

 analogues are known to function in nature either as precursors or products 

 in nicotinic acid metabolism, and there seems to be considerable variation 

 in the abilities of various species to utilize these analogues. In general the 

 activity of nicotinic acid is believed due to its conversion to nicotinic 

 acid amide and thence to Coenzymes I and II, and consequently sub- 

 stances that may be readily converted to nicotinic acid or nicotinic acid 

 amide may be expected to show nicotinic acid activity. Mueller's finding 

 that nicotinic acid is more potent than nicotinic acid amide for diphtheria 

 organisms, 109 and the discovery by Dorfman et al. 110 that nicotinic acid 

 amide is more potent than Coenzymes I or II for dysentery organisms, 

 while in discord with this view, do not prove unequivocally that it is 

 untenable, but rather indicate the fastidious nature of certain cells with 

 regard to their nutritional source of building blocks for intracellular 

 coenzymes. 



In order to obviate an unduly lengthy discussion regarding the activity 

 of these derivatives for various species, the available information is sum- 

 marized in Table 14. The effects of a large number of synthetic pyridine 

 derivatives which do not occur in nature have been reviewed adequately 

 in the literature m and in Chapter VI D of this monograph. Much of the 

 tryptophan-nicotinic acid interrelationship has been worked out with 

 Neurospora mutants, and for that reason data are included to show the 

 metabolites which have been found active for some Neurospora mutants. 



Few quantitative interrelationships are known. It is generally true that 

 nicotinic acid and nicotinic acid amide are about equally active, though 

 exceptions exist, particularly among bacteria. The drug coramine is not 

 nearly as active as nicotinic acid, but seems to be sufficiently active to be 

 an effective therapeutic agent in man. /3-Picoline has a low activity, but 

 the /?-methyl group can apparently be oxidized to niacin. For rats on a 

 corn diet, Krehl 7T found 1.0-1.5 mg nicotinic acid to be approximately 



