IV NUCLEOTIDE SYNTHESIS lOI 



ATP 



1) UTP + NHj » CTP + ADP + Pi 



The reverse process, the formation of uracil compounds from cytosine deriva- 

 tives, has been readily demonstrated in most animal tissues, microorganisms, and 

 yeast (Wang et al., 1950; Wang and Lampen, 1952; Friedkin, 1953): 



2) Cytidine > uridine + NH3 



E. coli 



3) Deoxycytidine — -^ deoxyuridine + NH3 



yeast 



4) 5-Methylcytosine > thymine + NH3 



yeast, E. coli 



5) Cytosine > uracil + NH3 



soil bacteria 



It Is to be noted that the combined action of cytidine (or deoxycytidine) deaminase and 

 uridine (or deoxyuridine) phosphorylase on cytidine would result in the formation of 

 uracil, thereby simulating "cytidine phosphorylase" activity (Manson and Lampen, 1953). 

 Deoxycytidine deaminase may be of importance in connection with the formation of 

 deoxyuridine, a thymidine precursor. 



7. Trans-N-glycosidation 



During a study of pyrimidine metabolism in Lactobacillus helveticus McNutt 

 discovered a group of enzymes which catalyze the following type of reaction 

 (McNutt, 1952; Lampen, 1952): 



Purine deoxyriboside + pyrimidine * — ^ purine + pyrimidine deoxyriboside 



The reaction takes place between two purines, two pyrimidines, or a purine 

 and a pyrimidine and provides a mechanism whereby purines or pyrimidines can 

 be incorporated into deoxyribosyl linkage. Nucleoside phosphorylase, on the 

 other hand, is not detectable in this organism. Table 8 shows some of the com- 

 pounds which react with adenine deoxyriboside or thymidine. The enzymes are 

 also present in other lactic acid bacteria. 



TABLE 8 



FORMATION OF DE OX YRIB OSIDES BY TRANS- N-GLYCOSIDATION 



+ guanine / + guanine deoxyriboside 



+ hypoxanthine I + hypoxanthine deoxyriboside 



AJ„ • 1 -u -J ^ + xanthine 1 • '+ xanthine deoxyriboside 



Adenine deoxyriboside , . * — r adenine ' ... ' 



I + thymine \ + thymidine 



+ uracil 1 + deoxyuridine 



+ 5-methyluracil \ -\- 5-methyl cytosine deoxyriboside 



+ xanthine , + xanthine deoxyriboside 



rj^i -J- 1 + adenine .1 • )+ adenine deoxyriboside 



Ihymidine . ' — ' thymine . , ' ., . , 



J + guanine J + guanine deoxyriboside 



+ hypoxanthine + hypoxanthine deoxyriboside 



Literature p. 124 



