330 



GEORGE W. CROSBIE 



HOCH^O. 



■\j_j/O.PO^H2 



OH OH 



ATP 



ADP 



HjOgPOCHz^O 



OH OH OH OH 



P-P" OH OH 



Fig. 2. The uridine phosphorylase (A), uridine kinase (B), and uridine-5'-phos- 

 phate pyrophosphorylase (C) reactions. 



This concept is further supported by the occurrence of the enzymes asso- 

 ciated with UNA synthesis in the same high speed cellular supernatant 

 fraction. 



Reichard and Skold 67 have also reported the occurrence of uridine phos- 

 phorylase and uridine kinase in acetone powder extracts of Ehrlich ascites 

 tumor. The extracts possessed in addition a feeble uridine-5'-phosphate 

 pyrophosphorylase capable of condensing uracil and 5-phosphoribosyl- 

 pyrophosphate (Fig. 2). Uridine-5'-phosphate pyrophosphorylase is ap- 

 parently absent in rat liver. 



Crawford et al. b8 have investigated uridine-o'-phosphate synthesis in ex- 

 tracts of alumina-ground cells of a number of species of Lactobacilli. A 

 clear correlation between pyrimidine growth requirements and the presence 

 of a specific nucleotide pyrophosphorylase has been obtained. Thus Lacto- 

 bacillus bifidus which requires either uracil or orotic acid for growth yields 

 an extract containing nucleotide pyrophosphorylase activities towards 

 orotic acid and uracil. The purified uracil enzyme is not active with orotic 

 acid. Lactobacillus arabinosus which in certain growth phases required uracil 

 specifically for growth had during this period an enzyme for uracil but not 

 orotic acid. L. bulgaricus 09, which utilizes orotic acid but not uracil for 

 growth, yields an enzyme active toward orotic acid but not uracil. Canella- 



57 P. Reichard and O. Skold, Acta Chem. Scand. 11, 17 (1957). 



58 I. Crawford, A. Romberg, and E. S. Simms, /. Biol. Chem. 226, 1093 (1957). 



