408 THE BIOCHEMISTRY OF B VITAMINS 



have a decreased D-amino acid oxidase activity, which is increaed by 

 the addition of riboflavin dinucleotide, indicating that the apoenzyme is 

 present and only the coenzyme deficient. 75 In ariboflavinosis there are, 

 moreover, some signs of a water metabolism derangement similar to those 

 that have been observed in pantothenic acid deficiency (p. 424) , 76 In 

 hens and dogs that have died of ariboflavinosis there is an increased liver 

 fat content, and a high fat diet seems to aggravate the symptoms of 

 riboflavin deficiency in rats. 



It has been suggested that the oxidative role played by riboflavin in the 

 normally avascular cornea is counteracted in deficiency by supply of the 

 needed oxygenation by vascularization. It has been reported that in 

 riboflavin deficiency there is an increased magnesium requirement. 77 

 Since riboflavin and thiamine have been reported to have limited sparing 

 actions on each other and since magnesium is involved as a cofactor with 

 thiamine, it is possible that the magnesium effect is due to increased 

 thiamine activity. B vitamins have been reported to reverse atabrine 

 toxicity for rats, 78 and riboflavin may be active in this regard, as it is 

 in reversing atabrine inhibition in the tryptophanase reaction. 79 Generally, 

 however, it is apparent that there is little true understanding of the 

 biochemical picture in ariboflavinosis. 



Nicotinic Acid. Nicotinic acid deficiency occurs most frequently in 

 the form of pellagra, although classical pellagra is not purely a nicotinic 

 acid deficiency. This disease is common throughout the world, frequently 

 compounded with beriberi and other avitaminoses, and at one time or 

 another has been either endemic or epidemic in nearly every area except- 

 ing northern Europe. It is endemic in the southeastern United States, 80 

 in South Africa, 9 - 81 and in some other tropical and semitropical areas of 

 the world. It is considered in many respects to be more dangerous than 

 beriberi, and is certainly the major clinical avitaminosis encountered in 

 the United States. It is considered to be an economic disease, as Drum- 

 mond says, a matter of pounds, shillings, and pence. 82 



Most generally pellagra is associated with populations in which corn 

 is a staple in the diet, just as polished rice is in beriberi. As previously 

 mentioned (p. 279), this appears to be due to the low nicotinic acid and 

 tryptophan content of the corn, coupled with the possible presence of a 

 pellagragenic factor in the corn. Pellagra and other somewhat atypical 

 forms of niacin deficiency also occur, however, under other circumstances 

 when the dietary levels of niacin and tryptophan are low. 83 



As with thiamine, nicotinic acid deficiency is a frequent result of 

 chronic alcoholism and has been observed secondary to drug addiction. 84 

 It is readily apparent, however, that there are many factors other than 

 nutritional ones which are secondarily involved in the etiology of pel- 



