WAGMAN AND TRAWICK 13 



The stabilizing effect of the dialyzable material, which is tentatively desig- 

 nated "decomposition inhibitor" (DI), was further demonstrated as follows. 

 After overnight dialysis of 1 volume of extract solution against 4 volumes of 

 water, the dialysate was lyophilized and reconstituted to four-fifths of the vol- 

 ume of extract used. This procedure yields a solution, which we shall refer 

 to as buffer-DI, whose concentration of dialyzable material is roughly equal to 

 that of the original extract. The stabilizing effect of the DI was then observed 

 by comparing the sedimentation behavior of fresh extract solutions dialyzed 

 against buffer and buffer-DI, respectively. As is shown in figure 3, the DI 

 effectively prevented the disappearance of 40 S component. 



The nature of the stabilizing substance is not clear. An analysis of the di- 

 alyzable material indicates the presence of peptides and nucleotides as well as 

 trace amounts of magnesium, iron, and other metals usually found in bacterial 

 extracts. Metal ions appear to be ruled out as the active substance, for the sta- 

 bilizing effect is lost by heating the buffer-DI for 5 minutes at about 90° C. 



Purification of 40 S Component. It now appears that the early difficulties in 

 fractionating the 40 S component were due to a procedure which separates that 

 component from the stabilizer. By slightly modifying the original fractionation 

 scheme, the 40 S component was prepared in a relatively high state of purity 

 and stability. The pellets, after each of two successive centrifugation steps, were 

 redissolved in previously prepared buffer-DI. Figure 4 shows a comparison of 

 preparations, from a single batch of cells, obtained by this and the previous 

 methods. The sedimentation patterns demonstrate the degree of purity with 

 which it is possible to obtain the 40 S component, and illustrate the activity of 

 the DI. 



Physicochemical Properties. An analysis of the fractionated material indicated 



U 



Extract 



MM 



Extract dialyzed against: 

 Buffer Buffer-DI 



Fig. 3. Sedimentation diagrams illustrating the protective effect of the dialyzable stabi- 

 lizer on the 40 S component in E. coli extracts. 



