476 



CHEMICAL A O F. NTS 



Tetrachloro-p- 



benzoquinone 



(Chloranil) 



2,3-Dichloro-l,4- 



naphthoquinone 



(Dichlone) 



(CH 3 ) 2 — N 



C=< 



)=N— (CH 3 ) 2 — cr 



Malachite green 

 Figure 10. Fungistatic quinonoid compounds. 



that appropriate hyclroquinones, themselves non-toxic, may be con- 

 verted to toxic quinones. Thus, 2,3-dichloro-l,4-naphthohydroquinone 

 inhibits Monilia laxa, presumably because it is oxidized by the fungus 

 to the corresponding naphthoquinone; esters of the hydroquinone are 

 first hydrolyzed, then oxidized (56). 



Detoxification of quinones would be expected of a fungus which 

 forms melanin pigments; StempJiylium sarcinaeforme, which is nor- 

 mally black-pigmented, appears to convert many quinones to non-toxic 

 products (347). 



The reactivity of quinones is so great that more than one mode of 

 action may easily be envisaged. Although any quinone affects the oxi- 

 dation-reduction potential, it does not seem possible to correlate either 

 bacteriostatic or fungistatic effects with this property (266, 321, 434). 

 As a,/?-unsaturated ketones, quinones can react with both sulfhydryl 

 and amino groups (372), and these possibilities have enlisted consid- 

 erable interest. 



Quinones react, by addition, with simple thiols (212, 292). Corre- 

 spondingly, the antimicrobial activity of quinones is often reversible 

 by sulfhydryl compounds (70, 121). However, we have already noted 

 that thiol reversal is not by itself sufficient proof of the nature of the 

 in vivo reaction. Many of the enzymes known to depend upon sulfhy- 



