192 THE BIOCHEMISTRY OF B VITAMINS 



min component, is bound in such a way that it is not released by the 

 ordinary methods currently used for preparing samples for microbiologi- 

 cal assay. Acid hydrolysis of the coenzyme did, however, yield appreciable 

 amounts of /3-alanine. 256 The coenzymatic activity of preparations of 

 various degrees of purity paralleled the yS-alanine content. It was also 

 shown that pantothenic acid could be liberated in its uncombined form 

 by use of a combination of a phosphatase and an enzyme obtained from 

 liver. 256, 25T 



The presence of pantothenic acid in this coenzyme established at least 

 one function of this vitamin, and indicated its involvement in reactions 

 in which acetic acid is utilized. It was realized, however, that neither of 

 the rather specialized reactions studied could account for the general 

 importance of the vitamin. This led to the subsequent demonstration of 

 the essentiality of the pantothenic acid-containing coenzyme for a number 

 of reactions of general importance in carbohydrate and fat metabolism 

 where tracer studies and investigations of acetate metabolism in bacteria 

 had indicated involvement of acetic acid. This coenzyme is now usually 

 referred to as coenzyme A (A for acetylation) , and will be so designated 

 in this discussion. 



The Chemical Structure of Coenzyme A. The structure of coenzyme 

 A has not yet been announced. The rate at which it diffuses through 

 sintered glass membranes indicates that its molecular weight probably 

 lies between 750 and 850. 258 A preparation of the coenzyme containing 

 11 per cent pantothenic acid, contained 9 per cent phosphorus, 18 per cent 

 adenine, 22 per cent pentose and some cysteine. On the basis of its panto- 

 thenic acid content and apparent molecular weight, this preparation was 

 only 50 per cent pure, but its analysis does indicate the presence of 

 adenylic acid. Glutamic acid is probably an additional constituent, since 

 it is essential for the biosynthesis of a pantothenic acid complex, 259 which 

 is believed to be identical with a product obtained during the enzymatic 

 degradation of the coenzyme. 258 Studies of the enzymatic degradation of 

 the compound indicate that there are at least two linkages which must 

 be cleaved before pantothenic acid is liberated. Both an intestinal phos- 

 phatase and an enzyme present in liver extract must be allowed to act 

 upon the molecule before the coenzyme will be active in the microbiologi- 

 cal assays usually employed. Either enzyme alone renders the coenzyme 

 inactive (each producing a different product), but neither enzyme by 

 itself liberates panthothenic acid. 257 



Assay Methods. The microorganisms commonly employed in B vita- 

 min assays cannot utilize coenzyme A. 256 Acetobacter suboxydans, which 

 responds very slowly to pantothenic acid, has been shown to grow rapidly 

 in the presence of a pantothenic acid conjugate (PAC) concentrated from 



