O MAURICE J. HESSMAX 



kinase 

 Dt^oxyril)08e-5-pho8phato + ATP — > 



5-phosphodeoxyribosyl-l-p>Topho8phat€ + AMP 



5-Phospho(leoxyribosyl-l-pyrophosphate + base — » deoxjTiucleotide + p^Tophosphate 



Although these reactions were looked for (Kornbcrg, 1957) no evidence 

 for such a pathway was found. 



B. SYNTHESIS OF THYMIUYLIC ACID 



Tracer experiments in whole-cell systems indicated tiiat tlie general 

 pathway for the synthesis of thymidylic acid involved the condensation 

 of an "active" 1 -carbon unit, probably a derivative of folic acid, with a 

 derivative of undine or cytidine (for review see Crosbie, 1960). 

 Friedkin and Koiiiherg (1957) described a cell-free preparation from 

 E. coli which converted dcoxyuridylate to thymidine triphospiiate in 

 the presence of tetrahydrofolic acid (THFA), serine, and ATP. The 

 properties of the system are described in Table III. The role of 



TABLE III 



CONVERSIO.N OF DeoXYURIDYLIC AcID TO THYMIDINE TrIPHOSPH.^TE" 



Cpm 



on Xorit 



Experiment 1 



Complete system* 1()50 



zero time 24 



minus THFA 47 



- serine 480 



- ATP 51 



- extract 212 



- Mg 30 



- pyridoxal phosphate 1500 



Experiment 2 

 Complete system 



+ serine + THFA 187U 



- serine + THFA 470 

 Complete system 



+ serine + hydroxymothyl THFA lfi5() 



- serine + hydroxymothyl THF'A 1210 



° From Friedkin and Kornberg (1957). 



'' The romplete system (^.325 /^liters; pH 7.4) contained 0.011 /xmoles of deoxyuridine- 

 5'-phosphate labeled with P^^ (2500 cpm), 2.3 ^nioles of ATP, 5.7 Mmoles of MgCh, 

 11.4 /iimoles of L-serine, 0.1 /xniole of THFA or A'^^-hydrox^-methyl THFA, 0.5 ^mole of 

 cysteine, 2.5 ^moles of inorganic orthophosphate, 0.1 /tmole of pyridoxal phosphate, 

 21 /iimoles of tris, thymidylate kinase, and an extract of E. coli treated with Dowex-1- 

 formate. 



