Effects of 8-Azaguanine on the Specificity of Protein 

 Synthesis in Bacillus cereus 



H, Chantrenne 



Laboratory of Biological Chemistry, Faculty of Sciences, 

 University of Brussels, Belgium 



If 8-azaguanine is added to a growing population of Bacillus cereus, 

 the rate of increase of the optical density of the bacterial suspension is 

 reduced by about 50% [i, 2, 3]. Such an observation is usually expressed 

 in the following way: "azaguanine reduces the rate of growth of the 

 bacteria". This statement can be misleading; it depends what is meant 

 by "growth". A closer study of the effects of 8-azaguanine revealed the 

 following facts [3, 4, 5]. The analogue inhibits the increase of bacterial dry 

 weight by 40 to 50°,,- Protein synthesis is almost completelv suppressed, 

 whereas the formation of cell wall material, including the peptides it 

 contains, is practically untouched. The synthesis of ribonucleic acid can 

 be stimulated, unaffected, or slightly depressed depending on experimental 

 conditions, especially aeration. Xo effects are observed on the synthesis of 

 DNA when low concentrations (4 /xg./ml.) of azaguanine are used; a 

 partial inhibition slowly establishes in the presence of higher concentrations 

 (40 /xg./ml.) of the drug. 



The formation of various essential cell constituents is thus very 

 differently affected by azaguanine, with the obvious result that the gross 

 composition of the bacteria is progressively changed. On the other hand, 

 the number of viable bacteria, i.e. the number of bacteria which are able 

 to form a colony when plated on a normal medium, ceases to increase 

 within 20 min. of the addition of azaguanine; it then stays constant for 

 about 2 hr. before dropping sharply. Therefore, the changes in chemical 

 composition of the bacteria which are caused by 8-azaguanine are not 

 immediately lethal. Recovery of the bacteria from the toxic effects of the 

 analogue is a slow and progressive process. 



The inhibition of protein synthesis in B. cereus is fully expressed 

 within about 10 min. of the addition of azaguanine (36 /xg./ml.). If guano- 

 sine (135 /xg./ml.) is added together with azaguanine, it completely protects 

 the bacteria against the analogue. If added not later than 30 min. after 

 azaguanine, guanosine rapidly restores the synthesis of proteins. But this 



