MARINE 

 BIOiaGiCAL 

 LASORATORY 



LIBRARY 



WOODS HOLE, MASS. 

 W. H. 0. I. 



CHAPTER 22 



Biosynthesis of Pentoses 

 GERTRUDE E. GLOCK 



Page 



I. Introduction 248 



II. The Hexosemonophosphate Oxidative Pathway as a Source of Pentose 

 Phosphate 248 



1. Early Investigations 248 



2. Recent Work on the Identification of Pentose Phosphates 249 



a. Ribose-5-phosphate 249 



b. Ribulose-5-phosphate 250 



3. Metabolism of Ribulose-5-phosphate 251 



a. Formation of Triose Phosphate 251 



b. Synthesis of Sedoheptulose-7-phosphate and Hexose Monophos- 

 phate 252 



III. Pentose Phosphate Formation in Photosynthesis 254 



IV. Significance of the He.xosemonophosphate Oxidative Pathway 256 



1. Distribution 256 



2. As an Alternative Pathway to Glycolysis 257 



3. As a Source of Pentose Phosphate for Nucleic Acid Synthesis 261 



V. Other Methods of Biosynthesis of Pentose Phosphates 262 



1. Condensation of C2 and C3 Units 262 



a. Synthesis of Xyloketose-1 -phosphate 262 



b. Synthesis of Deoxyribose-5-phosphate 263 



c. Synthesis of Ribulose-5-phosphate 263 



2. Decarboxylation of Uronic Acids 264 



3. In vivo Synthesis from Noncarbohydrate Sources 265 



4. Miscellaneous 265 



VI. Interconversion of Pentose Phosphates and Pentoses 266 



1. Phosphopentose Isomerase 266 



2. Phosphopentomutases 266 



a. Phosphoribomutase 266 



b. Phosphodeoxyribomutase 267 



3. Pentose Isomerases 267 



VII. Metabolism of Pentoses 268 



1. In Microorganisms 268 



a. Oxidation of Pentoses 268 



b. Fermentation of Pentoses 269 



c. Fermentation of Deoxyribose 271 



2. In Mammals 271 



VIII. Addendum 272 



247 



