608 PANTOTHENIC ACID 



° Pantothenic acid, 2-niercaptoethylamine, 3-phosphoric acid, adenosine, — 5H2O; molecular weight 767. 

 ^ Liberated by prostate phosphomonoesterase. 



acetyl-CoA, may be purified easily by resin chromatography. She obtained 

 in this manner practically pure acetyl-CoA. 



A very convenient method for a preparation of various CoA derivatives 

 was recently described by Simon and Shemin,^^" using the great affinity of 

 SH-compound for acid anhydrides. For example, they synthesized, in 

 aqueous solution, succinyl-SCoA from CoA-SH and succinic anhydride in 

 excellent yield, using only a slight excess of anhydride. This reaction is very 

 generally applicable. 



4. The Structure of CoA 



Analytical data on a nearly pure CoA preparation^'' are represented in 

 Table I. The data agree mth the composition of pantothenic acid, thio- 

 ethanolamine, adenosine, and three phosphates, minus 5H2O. In con- 

 junction mth this analytical data, the results of structural analysis pre- 

 sented in the previous paragraphs lead to the formulation shown in Fig. 5. 

 (This structure is now definitely established by analysis as well as by en- 

 zymatic synthesis.) 



To summarize, the biosynthesis of CoA from pantothenic acid involves 

 the following steps: 



1. Pantetheine, by condensation of pantothenic acid and cysteine, with 

 subsequent decarboxylation. 



2. Phosphorylation of pantetheine in the 4'-position by ATP. This reac- 

 tion is catalyzed by Kinase I, which was partially purified from pigeon liver 

 extract. 



3. Condensation of pantetheine-4'-phosphate and ATP, with elimina- 

 tion of inorganic pyrophosphate, by a condensing enzyme in pigeon liver 

 extract. The resulting product is "dephospho-CoA" also obtained from 

 CoA by dephosphorylation with prostate phosphomonoesterase. 



4. The final step is catalyzed by Kinase II, Avhich phosphorylates de- 

 phospho-CoA in the 3-position on the ribose part of adenylic acid. 



"« E. J. Simon and D. Shemin, J. Am. Chem. Soc, 75, 2590 (1953). 



