III. BIOCHEMICAL SYSTEM 607 



in the process of isolation.^^ Such S-S- cross-links also contaminate all 

 cruder CoA preparations."- ^* 



Govier and Gibbons*^ obtained an independent support for the presence 

 of pantethine in CoA. They found that aged pigeon liver extract could 

 synthesize small but appreciable amounts of CoA from synthetic pan- 

 tethine + ATP. Lexdntow and Novelli'^ in this laboratory recently found 

 that such a synthesis occurs much more readily in very fresh liver extracts. 



3. ACETYL-CoA 



The analysis of various acetylation systems involving CoA had led to 

 the recognition of its acetyl carrier function, a shuttling back and forth 

 between acetyl donor and acceptor systems.^^- ^^' "" Recently, Lynen and 

 Reicherf^' ^* succeeded in isolating acetyl-CoA in substance from yeast. 

 They furthermore became aware of the possibility that the SH-group in 

 CoA^^' ^* may be the point of attachment of the acetyl group. In confirma- 

 tion, they could show in a brilliant piece of work that acetyl-CoA, which is 

 nitroprusside negative, becomes SH-positive by such alkali treatment as 

 is known to split the mercaptoesters. The nature of the acetyl-S-CoA link 

 was further verified by the lability of the acetyl group in CoA to mercuric 

 salt, a rather specific property of mercaptoesters.^" It reminds one interest- 

 ingly enough of the similar behavior of enol phosphate, which likewise is 

 easily split catalytically by mercuric salts. 



Lynen and Reichert also showed that, with the acceptor enzyme of liver 

 extract, acetyl-CoA donates acetyl to sulfanilamide, and that SH- is 

 liberated by this enzymatic acetyl transfer. Acetyl-CoA was furthermore 

 identified as acetyl donor in citric acid synthesis.^^ 



More recently, Stadtman,^^ in continuation of earlier experiments on 

 transacetylase, worked out a rather efficient enzymatic method for the 

 preparations of acetyl-CoA. He used acetyl phosphate with the trans- 

 acetylase, for example, of Clostridium kluyveri, as the acetyl donor system, 

 with which CoA can be preparatively acetylated. Acetyl phosphate is 

 destroyed by heating at a pH of 4.5, whereas acetyl-CoA is stable. M. E. 

 Jones, in our laboratory, found that the product of enzymatic acetylation, 



» G. M. Brown and E. E. Snell, Proc. Soc. Exptl. Biol. Med. 77, 138 (1951). 



*^ J. D. Gregory and F. Lipmann, Abstr. Papers 12th Intern. Congr. Pure and Appl. 



Chem. New York, p. 74 (1951). 

 <« T. C. Chou, G. D. Novelli, E. R. Stadtman, and F. Lipmann, Federation Proc. 9, 



160 (1950). 

 « E. R. Stadtman, Federation Proc. 9, 233 (1950). 

 ^8 F. Lynen and E. Reichert, Angew. Chem. 63, 47 (1951). 

 " F. Lynen, E. Reichert, and L. Rueff, Ann. 574, 1 (1951). 

 60 G. Sachs, Ber. 54, 1849 (1921). 

 " S. Ochoa, J. R. Stern, and M. C. Schneider, /. Biol. Chem. 193, 691 (1951). 



