CHAPTER 24 



Biosynthesis of Nucleosides and Nucleotides 

 F. SCHLENK 



Page 

 I. Introduction 309 



1. Historical 309 



2. Significance of Nucleosides and Nucleotides as Intermediates of Poly- 

 nucleotide Synthesis 310 



II. Biosynthesis of Nucleosides 311 



1. Purine Riboside Phosphorylase 311 



2. Purine Riboside Hydrolases 314 



3. Purine Deoxyriboside Nucleosidases 315 



4. Pyrimidine Riboside Phosphorylase 315 



5. Pyrimidine Nucleoside Hydrolases 316 



6. Pyrimidine Deoxyriboside Phosphorylase 318 



7. Nucleoside -A^-transglycosidases 319 



8. Interconversion of Nucleosides and Nucleotides by Reactions other than 

 Transglycosidation 321 



a. Inosine ;=^ Adenosine 322 



b. 5-Adenylic Acid Deaminase 322 



c. Amination of Inosine and Inosinic Acid 322 



d. Guanylic Acid Deaminase 323 



e. Cytidine Deamination 323 



f. Decarboxylation of Orotic Acid and Its Homologues 324 



g. Formation of 5-Methyldeoxycytidine and Thymidine 324 



III. Biosynthesis of Nucleotides 324 



1. Experiments with Labeled Nucleosides and Nucleotides 325 



2. Enzymic Reactions of Nucleotide Metabolism 327 



a. 5-Nucleotidase and 3-Nucleotidase 327 



b. Adenosine Phosphokinase 328 



c. Nucleotide-A^-ribosidase 329 



d. Enyzmic Phosphorylation of Nucleosides by Phosphate Transfer . . 330 

 IV. Biosynthesis by Reaction of Pentose or Pentose phosphate with Incomplete 



Pyrimidine and Purine Systems 331 



V. Role of B-Vitamins in Nucleoside and Nucleotide Synthesis 334 



1. Vitamin B12 334 



2. Citrovorum Factor (Leucovorin, Folinic Acid SF, Coenzyme F) .... 335 



3. p-Aminobenzoic Acid and Folic Acid 336 



VI. Addendum 336 



I. Introduction 



1, Historical 

 It is not surprising that an adequate concept of the role of nucleosides or 

 nucleotides in nucleic acid metabolism was not developed by the early in- 



309 



