BIOSYNTHESIS OF NUCLEOSIDES AND NUCLEOTIDES 337 



Such a phosphate shift may be of general importance as indicated by the 

 discovery of the reaction:'^" 



Adenosine triphosphate + inosine diphosphate ;=i ,^., 



adenosine diphosphate + inosine triphosphate 



A connection of uridine triphosphate with co-waldenase is indicated by the 

 reaction :^'^'^' 



Uridine diphosphate glucose (gahactose) + pyrophosphate ;=i ,na\ 



uridine triphosphate + a-glucose-1-phosphate (a-galactose-1-phosphate) 



Nucleoside Metabolism 



A hydrolytic ribonucleosidase has been obtained from fish muscle by 

 Tarr.^^^ After 650-fold purification it was found to act on purine ribosides 

 and cytidine, but not on uridine. Continued studies by Friedkin^^^ on py- 

 rimidine deoxyriboside phosphorylase from calf kidney have shown com- 

 plete lack of reactivity of orotic acid and 5-methylcytosine with deoxy- 

 ribose-1 -phosphate. However, in addition to the bases specified in equations 

 (8) and (9) (p. 318), some substituted synthetic pyrimidines showed mod- 

 erate activity."-^ 



5-Hydroxymethylcytosine 



The discovery of 5-hydroxymethylcytosine (Chapter 10) (16 to 17 moles 

 per 100 moles of DNA bases) in some bacteriophages (E. coli, T2 , T4 , and 

 Te , but not in Tb and T7) poses interesting questions.^*-'' The host cell does not 

 contain this base. It is not clear yet at what level (base, nucleoside, or nu- 

 cleotide) the conversion of host pyrimidine units into 5-hydroxymethyl- 

 cytosine occurs.'^' ■'•*^"'^^* 



Thymidine and Other Pyrimidine Compounds 



Sprinson and co-workers^*^ have extended their work on the formation 

 of the methyl group of thymine or thymidine. Experiments with 2,3- 

 deuterio-3-C^^-N^^-serine have led them to believe that formate is not an 

 intermediate, because both hydrogens accompany the /3-carbon in the trans- 

 it" P. Berg and W. K. Joklik, Nature 172, 1008 (1953); /. Biol. Chem. 210, 657 (1954). 

 >" H. L. A. Tarr, Federation Proc. 13, 309 (1954). 

 i« M. Friedkin and D. Roberts, /. Biol. Chem. 207, 257 (1954). 

 i«»F. Weygand, A. Wacker, and H. Dellweg, Z. Naturforsch. 7b, 19 (1952); D. B. 



Dunn, J. D. Smith, S. Zamenhof, and G. Griboff, Nature 174, 305 (1954). 

 !«'' R. L. Sinsheimer, Science 120, 551 (1954). 



1" G. R. Wyatt and S. S. Cohen, Nature 170, 1072 (1952); Biochem. J. 55, 774 (1953). 

 >" L. L. Weed and T. A. Courtenay, J. Biol. Chem. 206, 735 (1954). 

 '^ S. S. Cohen and L. L. Weed, /. Biol. Chem. 209, 789 (1954). 

 1" D. Elwyn, A. Weissbach, and D. B. Sprinson, J. Am. Chem. Soc. 73, 5509 (1951); 



D. Elwyn and D. B. Sprinson, /. Biol. Chem. 207, 467 (1954). 



