STRUCTURE AND ACTIVITIES OF CELLS 



Nicotinic acid, niacin, or the antipellagric vitamin, protects man against the 

 disease called pellagra, which was formerly very common in the Southern 

 states and found throughout the nation. Pellagra is characterized by skin 

 lesions, digestive disturbances, muscular weakness, and progressive impair- 

 ment of the nervous system, often ending in insanity. In 1914 it was proved 

 a dietary-deficiency disease. It has since been shown that pellagra probably 

 results from scarcity of several of the B-complex vitamins, including thiamine 

 and riboflavin. Education regarding proper diet and the medicinal use of 

 nicotinic acid have reduced the incidence of the disease. Other animals 

 exhibit pellagra-like symptoms; in dogs, the condition is called blacktongue. 

 Niacin is abundant in fresh meat, liver, yeast, milk, eggs, and fish. This 

 vitamin also functions in cellular oxidations, forming two coenzymes: co- 

 enzvme I, or diphosphopyridine nucleotide (DPN), and coenzyme II, or 

 triphosphopyridine nucleotide (TPN). These are involved in several diflferent 

 steps in carbohydrate metabolism (p. 36), and DPN is essential for vision 

 (see Fig. 4.16, p'. 108). 



Pyridoxine, vitamin B^;, was first found to be a dietary requirement for 

 rats in which it prevented dermatitis. It was later shown to be essential 

 for man, also, even though a deficiency disease for this vitamin has not been 

 identified. Yeast, whole grains, egg yolk, milk, and liver are good food 

 sources for pyridoxine. It plays an important role in various enzymatic 

 reactions in amino acid metabolism in the cell. 



Pantothenic acid is so widely distributed in food that, even on a restricted 

 diet, man apparently gets enough; a deficiency syndrome is not known. In 

 rats, mice, and chickens, however, deficiency leads to dermatitis and wide- 

 spread disorder in other tissues, suggesting a basic function in cellular 

 metabolism. Pantothenic acid contributes to the formation of an exceedingly 

 important compound known as coenzyme A. This coenzyme takes part in the 

 metabolism of carbohydrates, lipids including steroids, and proteins (p. 36). 



Biotin, or vitamin H, is necessary for the growth of various birds but is not 

 a dietary requirement for mammals, in which it is supplied by the intestinal 

 bacteria. The feeding of raw egg white to mammals produces a biotin 

 deficiency because the egg white combines with the biotin and renders it 

 ineffective as a vitamin. Diarrhea, dermatitis, and nervous disorders are 

 symptoms of biotin deficiency. 



A group of vitamins of the B complex is designated the folic acid group; 

 all are related to pteroyl glutamic acid. Folic acid is essential for growth in 

 higher animals. Fresh green leafy vegetables, kidney, and liver are rich food 

 sources. Intestinal bacteria also contribute to the supply of folic acid. Con- 

 sequently, administration of certain sulfa drugs which act directly on the 

 intestinal flora may contribute to a deficiency. Anemia is the most obvious 

 defect in animals with a folic acid deficiency. 



Knowledge of these growth substances has contributed to an understanding 

 of the mechanism of action of a group of drugs, the sulfonamides, in com- 

 bating bacterial infection. The various sulfonamides resemble para- 



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