IV. BIOCHEMICAL SYSTEMS 



141 



and oxidized casein) supplcnuMitcd willi lioniocyslinc, there is a relation- 

 sliip l)e(\veen homocystiiie, choline, PGA, and vitamin B12 recinirement.s 

 (Schaefer and Knowles-'-'). On .such a diet no growth takes place, and there 

 is a 100% incidence of renal hemorrhage. The effects of methyl donors, 

 vitamin B12 , and PC^iA are shown in Table III. The results clearly indicate 

 that choline alone or a combination of betaine plus aminoethanol will {)ro- 

 tect against renal hemorrhage in the absence of both vitamin B12 and P(JA. 

 On diets marginal in choline or lietaine neither B12 nor P(5A has any effect 

 on renal damage. Complete protection can be achieved with a comV)ination 



TABLE III 

 Effect of Vitamin B12 and PGA ox the Utilization of Betaine, Choline, and 



Aminoethanol 



of these two vitamins or by increasing the level of betaine or chohne. This 

 clearly shows that the requirements for PGA are higher on diets marginal 

 in choUne. 



Ahhough a combination of vitamin B12 and PGA affords complete pro- 

 tection against renal damage on diets marginal in choline, it does not pro- 

 duce a maximum growth response. Maximum growth is given only by 

 higher levels of choline supplemented with vitamin B12 , PGA having little 

 effect on growth at these levels of choline. 



A similar effect of PGA and B12 on lipotropism has l)een noted in rats 

 (Schaefer e< a/.^"). Fatty livers were noted in rats receiving 0.1 % of choline 



" A. E. Schaefer and J. L. Knowles, Proc. Soc. Exptl. Biol. Med. 77, 655 (1951). 

 «» D. R. Strength, E. A. Schaefer, and W. D. Salmon, J. Nutrition 45, 329 (1951). 



