12 MAURICE J. bp:.ssman 



the enzyme is called, is specific for dCMP and will not react with CMP, 

 deoxycytidine, cytidine, or cytosine. It is distinct from thymidylate 

 synthetase since it is much more stable in crude extracts of infected 

 cells than the latter enzyme and it is not inhibited by 5-fluorode- 

 oxyuridylate. 



In respect to its distribution, deoxycytidylate hydroxymethylase has 

 only been found in significant levels in extracts of E. coli infected with 

 T2, T4, or T6 bacteriophages. It is not detectable in uninfected cells, in 

 the viruses, or in cells infected with a virus which does not contain 

 5-hydroxymethylcytosine. Recently, Pizer and Cohen (quoted in Cohen, 

 1961), using very highly labeled formaldehyde in the enzyme assay, 

 have shown that less than 1 molecule of active deoxycytidylate hy- 

 droxymethylase is present per uninfected bacterial cell. These calcula- 

 tions are based on a molecular weight of 64,000 ± 9000, and a turnover 

 number of 1200 for the enzyme. It would appear then, that deoxycy- 

 tidylate hydroxymethylase is either present in uninfected bacterial cells 

 in an inactive form and is activated after infection or its formation is 

 induced by injection of tiie viral DNA. Experiments designed to test 

 these two alternatives tend to favor the latter, although no definitive 

 statement can be made. 



III. Phosphorylation of DEOXYRiBONUCLEOxroES 



A. DEOXYRIBONUCLEOSIDE MONOPHOSPHATE KINASES 



The name deoxyribonucleotide kinase has been given to a group of 

 enzymes which catalyze the following reaction: 



Deox>Tibonucleoside monophosi)hate + ATP ^ 



deoxyrihonucleoside diphosphate + A DP 



This classification is misleading because it ascribes a degree of specificity 

 to this group of enzymes which is not warranted. Both of the enzymes 

 in this category, which have been purified and studied in detail (deoxy- 

 cytidylate and deoxyguanylate kinases), catalyze the phosphorylation 

 of ribo- as well as deoxyribonucleotides. 



The occurrence of phosphorylated deoxyribonucleotides in animal 

 tissues was reported by Potter et al. (1957), who identified the di- and 

 triphosphates of deoxythymidine and deoxycytidine in the acid-soluble 

 fraction of thymus glands. Interestingly enough, these authors found no 

 evidence for the polyphosphates of the corresponding purine deoxyribo- 

 nucleosides. Sable et al. (1954) observed that rat liver mitochondria 

 actively oxidizing glutamate could fonn dADP and dATP from dA^NIP. 

 The demonstration of adenylate kinase in liver mitochondria (Siekevitz 



