NUCLEIC ACIDS AND RELATED COMPOUNDS 



237 



+ 2[h]; 



Most plant tissues have a higher concentration of TPN than of DPN the reverse 



of the situation in animal tissues. Very little free riboflavin is extractable from tissues. 

 It is largely in the coenzyme form, and this is rather tightly bound to proteins known as 

 flavoproteins. 



The functioning of uridine triphosphate (UTP) as a coenzyme for transfer of glycosyl 

 groups is discussed in Chapter 2. The functioning of coenzyme A in transfer of acyl groups 

 is discussed in Chapters 3, 5, 6 and 7. The complete structures of these two nucleotides 

 are given below. Neither one has been isolated in high purity from higher plants, but 

 there is ample evidence for their occurrence, and partially purified preparations have 

 been obtained. The pantothenic acid portion of coenzyme A is discussed separately in 

 Chapter 10. q 



goo 

 T t T 



CHjO POP OPOH 



I I I 

 OH OH OH 



UTP 



CHq OH 



t T I ^ I II II 



JHgO POP OCHjC CH-C NHCH2CH2CNHCH2CH2SH 



OH OH CHq 



H :P.:= PO3H2 



Coenzyme A 



Cytidine-5' diphosphate -choline has been isolated from yeast (11) where it acts as a 

 coenzyme to transfer choline for the synthesis of phosphatides (cf . Chapter 5). It has not, 

 so far, been isolated from higher plants. 



The nucleotides resemble the nucleosides in many of their properties but are dis- 

 tinguished by being strong acids. Pyrophosphate bonds found in several of the nucleotides 

 are readily cleaved by boiling with dilute acid. Thus two moles of orthophosphate are re- 

 leased from ATP. The monophosphates are much more resistant to acid hydrolysis. 



