ACETIC ACID AND ACETATE 267 



Lawrie^^ found that mercapturic acids resulted followmg the feeding of 

 iodobenzene to rats and rabbits, and Jaffe^"** observed the presence of these 

 acids in the urine of dogs following the administration of chlorobenzene. 

 An apparently analogous selenium mercapturic acid, in which selenium 

 replaced the sulfur of cysteine, was reported in selenium-treated dogs 

 foUo^vdng the administration of bromobenzene.^"^ A similar phenomenon 

 apparently obtains in selenium-poisoned steers; it was possible to remove 

 selenium practically completely from the blood by feeding bromobenzene. 

 Lemley^°"^ used bromobenzene feeding in the treatment of a case of selenium 

 poisoning in man, with excellent results. 



c. Acetylation of Choline. Acetylcholine, CHs-CO-OCHaCHa-Ni- 

 (CH3)3, is a potent compound, produced at the nerve endings when the 

 nerves are stimulated. As discussed in The Lipids, Vol. II, Chap. II, there 

 are several types of cholinesterases which can act on acetylcholine to 

 hydrolyze it and so to dissipate its main physiologic activity. However, 

 to effect the opposite reaction, which will result in the synthesis of acetyl- 

 choline, another enzyme system is reciuired. Xachmansohn and Machado^"^ 

 studied the mechanism of the acetylation of chohne. The presence of an 

 enzyme in cell-free brain extract, which was called choline acetylase, was 

 described bj^ Xachmansohn and collaborators. ^"'-^"^ In the presence of 

 ATP, choline acetylase can convert choline into acetylcholine. Lipmann 

 et al.^^^'^"^ showed that, as in other acetylations, pantothenic acid serves 

 as a coenzyme, presumably by virtue of its presence in CoA (see page 15). 



(4) Metabolic Reactions Involving Acetate 



Acetic acid is widely used in the sjmthesis of a variety of essential 

 components in the tissues. Although certain compounds required for the 

 functioning of the tissues, such as essential fatty acids, vitamins, and the 

 so-called essential amino acids, must be furnished as such from exogenous 

 sources, many of the remaining compomids may be synthesized from the 

 condensation of numerous small-sized units such as acetate, rather than by 

 the utilization and rearrangement of preformed large molecules. The 

 more important compounds which are known to originate more or less from 



1"! A. L. Moxon, A. E. Schaefer, H. A. Lardy, K. P. Du Bois, and O. E. Olson, J. Biol. 

 Chem., 132, 785-786 (1940). 



i«2 R. E. Lemley, J. Lancet, 60, 528-531 (1940). 



103 D. Nachmansohn and A. L. Machado, J. NeurophysioL, 6, 397-403 (1943). 



lo^ D. Xachmansohn and H. M. John, J. Biol. Cham., 158, 157-171 (1945). 



'"^ F. Lipmann, Harvey Lectures, 44, 99-123 (1948). 



los F. Lipmann, N. O. Kaplan, G. D. Novelli, L. C. Tuttle, and B. M. Guirard, J. Biol. 

 Chem., 167, 869-870 (1947). 



