342 GEORGE W. CROSBIE 



and deoxyuridine into DNA-thymidine was depressed as compared with 

 controls. Addition of Bi 2 in vitro to the deficient preparations stimulated 

 the incorporation. No B i2 effect on the utilization of cytidine for RNA- 

 pyrimidine nucleoside or DNA-deoxy cytidine formation could be detected. 

 Likewise thymidine incorporation into DNA-thymidine was not Bi 2 sensi- 

 tive. The results would appear to demonstrate a role for B 42 in the reactions 

 concerned with the "methylation" reaction rather than with deoxypentose 

 formation. The results are consistent with an involvement of Bi 2 in the syn- 

 thesis of a hydroxymethylfolic acid derivative (cf. Kisliuk and Woods 147b ). 

 The ability of B i2 to complex with formaldehyde is of interest in this con- 

 nection. 1470 ' Several discussions on the possible relationship between Bi 2 and 

 "1-C" metabolism have appeared recently. 147lM47g 



b. Biosynthesis in Cell- Free Systems 



The biosynthesis of thymidine-5'-phosphate (TMP) in cell-free systems 

 has recently been described by several groups. Friedkin and Romberg 98 

 have described a Dowex-1- (formate) -treated extract of E. coli which effects 

 a synthesis of thymidine-o'-triphosphate (TTP) from deoxyuridine-5'-phos- 

 phate (dUMP) in the presence of FH 4 , ATP, Mg++ and thymidylate 

 kinase. A^-Hydroxymethyltetrahydrofolic acid (N 10 — CH 2 OH— FH 4 ) could 

 substitute for serine. The TTP formed was assayed as a labeled phospho- 

 monoesterase-resistant charcoal-adsorbable nucleotide. The TTP was also 

 identified by ion-exchange chromatography and by degradation to thymi- 

 dine. 



Flaks and Cohen 112 and Birnie and Crosbie 148 have also studied thymi- 

 dylate synthetase activity in similar coliform extracts and have described 

 the FH 4 -dependent synthesis of TMP from (a) dUMP and formaldehyde- 

 C 14 112 and (b) deoxyuridine, ATP, Mg++, TPNH (or DPNH), and serine- 



3.Q14148 



Phear and Greenberg 149 have described a comparable mammalian system 

 [a Dowex-l-(chloride)-treated extract of thymus tissue] which couples de- 

 oxyuridine and formaldehyde-C 14 in the presence of FH 4 , ATP, Mg++, and 

 TPNH (rather than DPNH) to give TMP (together with a trace of thy- 

 midine formed from TPM through phosphomonoesterase action). The avail- 



U7b R. L. Kisliuk and D. D. Woods, .46s//-. VHth Intern. Congr. Microbiol., Stock- 

 holm (1958), p. 135. 

 i47c p Vohra, F. Lantz, and F. H. Kratzer, Arch. Biochem. Biophys. 76, 180 (1958). 

 147d E. Lester Smith, Nature 181, 305 (1958). 



147e H. R. V. Arnstein, jth Intern. Congr. Biochem., Vienna, (1958). 

 147f M. E. Coates and J. W. G. Porter, Ann. Rev. Biochem. 28, 439 (1959). 

 147 « J. M. Noronha and A. Sreenivasan, Biochem. J. 73, 732 (1959). 

 i« G. D. Birnie and G. W. Crosbie, Biochem. J. 69, IP (1958). 

 149 E. A. Phear and D. M. Greenberg, J. Am. Chem. Soc. 79, 3737 (1957). 



