PROSTHETIC GROUPS 35 



replaced by any known coenzyme. Preparations of the new 

 coenzyme A, as it was called, were found to contain panto- 

 thenic acid and their activity could be correlated with their 

 pantothenate content. The complete structure of coenzyme A 

 has not yet been determined and the complete molecule is 

 more complex than pantothenic acid alone. Coenzyme A is 

 now known to act in many reactions involving acetic acid, or 

 " acetyl phosphate," and is required by bacteria for the 

 acetylation of choline. Recently it has been shown that a 

 cell-free extract of Esch. coli will catalyse the condensation of 

 acetyl phosphate and oxalacetic acid to give citric acid 

 (see p. 153) and that the extract is activated by coenzyme A. 



CH3 H 



I I 



HOCH2— C C— CO— NH— CH2— CH2— COOH 



I I 



CH3 OH 



Pantothenic acid 



Biocytin 



The aspartic deaminase (see p. 162) of Esch. coli has been 

 shown to require a coenzyme which contains biotin and is 

 probably a compound of biotin and adenylic acid. The 

 complete structure is not yet known. A crystalline prepara- 

 tion of biocytin, which is a compound of biotin present in 

 yeast extracts, has now been made but it is not yet certain 

 whether this is identical with the aspartic co-deaminase or not. 

 



HN NH 



I I 



HC CH 



I I 



HgC CH— (CH2)4— COOH 



Biotin 



