350 ANIMAL BIOCHEMISTRY 



acetylase. After the stimulation has occurred, acetylchoHne might 

 collect at the synapses or connectors between cells and cause continuous 

 stimulation. This situation is avoided by the action of acetylcholine 

 esterase, which yields acetate and choline, thus terminating the stimu- 

 lation. Acetylcholine aids in controlling the heartbeat, for example. 

 Requirements for choline depend upon other dietary factors. High- 

 fat diets impose a greater need for choline than high-protein diets. 

 The latter provide methionine, which is also effective in methylations 

 and can replace much of the choline. Betaine can replace choline 

 completely, probably by conversion to it, and dimethylaminoethanol 

 replaces choline in the chick but not the rat. 



(CH3)3NCH2COO- (CHiO.NCH.CHoOH 



betaine diinethylaminoethanol 



When on normal diets, most animals are believed to require choline 

 in much larger amounts than is the case with the ordinary vitamins. 

 Chicks appear to need about 75 mg. daily, probably because the 

 substance is a component of fats and acetylcholine in addition to its 

 metabolic roles. Requirements have not been estimated for man. 

 Choline is abundant in liver, heart, kidney, tongue, other meats, yeast, 

 egg yolks, cereals, leafy vegetables, and a few vegetable oils such as 

 soybean oil. 



Deficiencies are not known in man except perhaps in pathologies 

 where there is excessive wastage of body protein as in severe burns, 

 wounds, or fevers. Some clinical use of choline has been made in 

 such cases. Deficient rats develop fatty livers, kidney lesions, paralysis, 

 anemia, hypertension, and edema, depending upon the severity and 

 duration of the lack. Chicks show many of these same manifestations 

 with another characteristic, one called perosis or slipped tendon. 



Inositol 



Hexahydroxycyclohexane occurs in nine stereoisomeric forms. Sev- 

 eral of these occur naturally, and one called 7n(?50-inositol is widely dis- 



HO OH 

 H 



'H H^ 

 vOH H/ 



OH 



HO 



H 



H OH 



meso-inositol 



tributed and of nutritional importance. This factor occurs in certain 



