290 H. J. ROGERS AND H. R. PERKINS 



a small nucleotide-linked mucopeptide accumulates which consists of 

 uridine diphosphate linked to N-acetylmuramic acid, alanine, glutamic 

 acid and lysine in the molar ratios of 1:1:3:1:1 [11]. Fragments of the 

 mucopeptide, namely uridine diphosphate-N-acetylmuramic acid and 

 uridine diphosphate-N-acetylmuramic acid linked to one molecule of 

 alanine, also occur. On the basis of the analytical similarity of the first of 

 these mucopeptides (excluding the nucleotide) with the cell wall muco- 

 peptide of their strain of staphylococcus, Strominger and Park [12] 

 suggested that the nucleotide-mucopeptide was a precursor of cell wall. 



The cell wall mucopeptide from our strain of organism [8, 13] prepared 

 by the Cummins and Harris [14] method differed in quantitative composi- 

 tion from that examined by Park and Strominger [12] which had been 

 prepared by the Salton and Home [14a] method. Such differences promp- 

 ted further investigation of the relationship between uridine nucleotide 

 linked compounds and cell wall mucopeptide synthesis. Also the com- 

 pounds isolated by Park [11] contained neither N-acetylglucosamine nor 

 glycine both of which are prominent components of the cell wall material 

 in all strains of staphylococci so far examined. 



A possible general way of examining the role of uridine compounds in 

 biosynthesis appeared to be to supply the cell with a pyrimidine analogue 

 which behaved sufficiently like the natural compound to be incorporated 

 into the small molecular weight compounds without these being able to 

 polymerize to form the macromolecules. The uracil analogue which 

 appeared most suitable for such a study was 5-fluorouracil. It had been 

 shown by Heidelberger and his colleagues [15, 16] that this uracil analogue 

 was converted by mouse tissues to the mono- di- and triphosphate nucleo- 

 tides and probably to fluorouridine-diphosphoglucose. Also on structural 

 grounds fluorouracil might be expected to behave more like uracil than 

 other analogues such as 5-bromo- and 5-iodouracil or 6-azauracil. 



The effect of 5-fluorouracil upon the synthesis of mucopeptides was 

 therefore studied and its action compared with that of other purine and 

 pyrimidine analogues. A full account of most of this work has already 

 appeared [20]. 



The effect of the compounds upon the biosynthesis of cell wall muco- 

 peptide was examined by measuring the rate of incorporation of [i-^^C]- 

 alanine, glutamic acid and glycine or [G-^*C]-lysine into washed cells of 

 Staphylococcus aureus strain 524/SC incubated in the presence of chloram- 

 phenicol under the conditions of Mandelstam and Rogers [8]. After incuba- 

 tion, the measurements of biosynthesis were made using material, prepared 

 from the cells, which was insoluble in hot trichloroacetic acid. It was 

 shown that incorporation into such material reflected cell wall mucopep- 

 tide synthesis by preparing the cell walls according to the method of 

 Cummins and Harris [14]. Of the following compounds only 5-fluorouraciI 



