556 G. SCHMIDT 



Page 



(1) Animal Thymidine Phosphorylase 605 



(2) Bacterial Uridine Phosphorylase 605 



2. Nucleoside Hydrolases 606 



a. Purine Nucleoside Hj'drolase of Yeast 606 



b. Uridine Hydrolase of Yeast 606 



c. Nucleoside Hydrolases of Lactobacillus pentosus 607 



3. Nucleotide-l'-phosphorylase 607 



4. Nucleotide-l'-pyrophosphorylase 607 



5. DPN Hydrolases 608 



VII. Xanthine Oxidase 609 



VIII. Enzymes Involving the Opening of the Purine Ring 614 



1. Inosinic Acid Transformylase 614 



2. Uricase 614 



IX. Enzymes Involving the Opening of the Pyrimidine Ring 619 



1. Reversible Degradation of Orotic Acid by Bacterial Enzymes .... 620 



a. Dihydroorotic Acid Dehydrogenase 620 



b. Dihydroorotase 621 



c. 5-Carboxymethylh}^dantoinase 621 



2. Conversion of Dihydrouracil and Dihydrothymine to /3-Amino Acids 



by Tissue Slices 621 



3. Degradation of Uracil and Thymine by Bacterial Enzymes 622 



a. Bacterial Oxidase of Uracil and Thymine 622 



b. Barbiturase 622 



X. Some Data Concerning the Intracellular Distribution of Enzymes of 



Nucleic Acid Metabolism 623 



1. Deoxyribonuclease 624 



2. Ribonuclease 624 



3. Intracellular Localization of Deoxyribonuclease I and Ribonuclease I 



in Pancreas 625 



4. Other Enzymes of Nucleic Acid Metabolism 625 



XI. Addendum (Concerning the Enzymic Formation of Nucleoside Di- and Tri- 

 phosphates) 625 



I. Introduction 



Owing to the large number of the several types of bonds between the 

 component groups in each nucleic acid molecule, various sequences of 

 reactions are theoretically possible for the catabolism and for the biosyn- 

 thesis of the nucleic acids. As in other metabolic fields, several different 

 specific enzymes exist in many instances for the cleavage or formation of a 

 given bond in nucleic acids or their derivatives. The pathway of nucleic 

 acid metabolism is thus not uniform. The biological significance of the 

 many alternative pathways of nucleic acid metabolism is not known at 

 present, but the highly specialized distribution and the high specificity of 

 some of these enzymes strongly suggests the idea that, in these instances, 

 the enzymic degradation products have specific biological functions. 



One generalization regarding the intermediary metabolism of nucleic 

 acids can be made, at least as a summary statement reflecting the present 



