278 THE BIOCHEMISTRY OF B VITAMINS 



level previously mentioned only after 12 weeks. 14 Still more direct evi- 

 dence was produced by Morgan et al., 6G who were able to produce a 

 vitamin B 6 deficiency in dogs on a 45.8 per cent casein diet in 79 to 123 

 days, but no deficiency on an 18 per cent casein diet for 169 to 190 days. 



Pantothenic acid is believed to function in the metabolism of carbo- 

 hydrates and more particularly in acetylation processes, and one might 

 expect that it might be less required in diets in which the main energy 

 component was protein. This expectation may be further strengthened by 

 the fact that amino acids function as precursors for both the /^-alanine 

 and pantoic acid moieties of pantothenic acid, and may thus encourage 

 synthesis in the intestine. Nelson and Evans 67 have recently shown that 

 rats raised on a pantothenic acid-deficient diet fare much better on a 

 high-protein diet (64 per cent casein) than on a lower one (24 per cent 

 casein) . 



The nutritional requirement for choline is greatly affected by the 

 protein intake of the diet, largely by virtue of the interrelationship 

 between choline and the amino acids serine and methionine. The precursor 

 function of serine for choline is discussed elsewhere (p. 89) in relation- 

 ship to the general cellular metabolism. The reciprocal relationships of 

 choline and methionine for growth and lipotropism 68 are most frequently 

 encountered in animal nutrition, however. Choline functions in the trans- 

 port of fats, and in the absence of an adequate supply a variety of symp- 

 toms, including a neutral fat type fatty liver, may develop. Methionine 

 may replace choline in the diet inasmuch as it serves as a source of methyl 

 groups for choline synthesis in vivo. Thus, in the presence of ample 

 serine, rats may grow at a normal rate (41.8 gms/21 days) and have 

 normal liver lipides (8.9 mg per cent) if the diet contains 1200 mg per 

 cent of methionine. 68 In the presence of 500 mg per cent of methionine, 

 however, the growth rate is only 23.8 gms/21 days and liver lipides are 

 24.7 mg per cent. Addition to this diet of 100 mg per cent of choline 

 restores liver lipides to normal but does not improve the growth rate. 

 These data taken from Treadwell's study are summarized in Table 13, 

 and are interpreted as meaning that on a choline-free diet, the methionine 

 requirement is 1200 mg per cent, of which about half is required for 

 lipotropism (i.e., choline synthesis) and half for growth. 



However, it should also be noted that starch, or some impurity therein 

 other than choline, has an appreciable effect in preventing the develop- 

 ment of the hemorrhagic kidneys found in young white rats on a choline- 

 deficient diet. 69 - 70 



For chick growth, a very similar relationship holds, as it does in a 

 variety of other animals. McKittrick 71 has found that the essential 

 choline (the limit beyond which reduction of choline cannot proceed with- 



