330 F. SCHLENK 



crude tissue enzymes. Their assumption of a glycosidic split without prior 

 removal of the phosphoric acid group (nucleotide- A^'-ribosidase action) is 

 based on the observation of a constant level of inorganic phosphate during 

 incubation, while according to the conventional scheme with nucleotidase 

 action as the first step there should be liberation of phosphate. However, 

 crude tissue preparations and long incubation times were used and the 

 carbohydrate phosphoric acid ester was not characterized.^^ 



In the light of more recent observations, another interpretation of these 

 experiments is possible. ^^ Guanylic acid may be split first by phosphatase 

 (eq. 21). The resulting guanosine is cleaved by phosphorolysis (eq. 22),. 

 and the resulting ribose-1 -phosphate is rearranged by mutase action to 

 ribose-5-phosphate (eq. 23) and to hexose-6-monophosphate*''^* and other 

 esters (see Chapter 22). 



Guanosine-3'-phosphate — ♦ guanosine + phosphate (21) 



Guanosine -|- phosphate —^ guanine -|- ribose-1 -phosphate (22) 



Ribose-1 -phosphate — > ribose-5-phosphate — > hexose-6-phosphate (23) 



No phosphate appears in the reaction medium under these circumstances, 

 provided reactions (22) and (23) are faster than (21). Proof of the existence 

 of 3-nucleotide-A''-ribosidase is lacking, at present; it would require the 

 isolation and characterization of ribose-3-phosphate. 



Other experiments in this category are those of Wajzer.^^-^'^ He reports 

 that the phosphorolysis of inosine by liver enzymes is attended by a sec- 

 ondary reaction leading to inosinic acid. Another set of his experiments deals 

 with the reaction of ribose-3-phosphate with hypoxanthine, adenine, and 

 guanine. The analytical techniques, however, are inadequate and the results 

 are partly hypothetical. 



It is tempting to assume that nucleotides are synthesized by the inter- 

 action of bases or base precursors with ribose-1 ,5-diphosphate. The pros- 

 pects^ of securing adequate amounts of this ester heralds important develop- 

 ments. 



d. Enzymic Phosphorylation of Nucleosides by Phosphate Transfer 



Brawerman and Chargaff^' have made important observations on the 

 formation of nucleotides by phosphate transfer; this process is catalyzed by 

 a phosphatase obtained from a commercial preparation of malt diastase. 

 In the presence of sodium phenyl phosphate as phosphate donor it converts 

 ribose and deoxyribose nucleosides into the nucleotides. Inorganic phos- 



" F. Schlenk, Advances in Enzymol. 9, 455 (1949). 



85 M. J. Waldvogel and F. Schlenk, Arch. Biochem. 22, 185 (1949). 



"J. Wajzer, Arch. set. physiol. 1, 493 (1947). 



" J. Wajzer and F. Baron, Bull. soc. chim. biol. 31, 750 (1949). 



88 H. Klenow and B. Larsen, Arch. Biochem. and Biophys. 37, 488 (1952). 



99 G. Brawerman and E. Chargaff, /. Am. Chem. Soc. 75, 2020 (1953). 



