EFFECTS ON VARIOUS METABOLIC SYSTEMS 



493 



provide useful information not only on the subject of multi-inhibition but 

 also on the individual actions of the two types of inhibitor. 



EFFECTS ON VARIOUS METABOLIC SYSTEMS 



Very little is known of the effects of the quinones on lipid, protein, or 

 nucleic acid metabolism. Maselli and Nord (1949) claimed that naphtho- 

 quinones suppress lipid formation in Fusarium lini at very low concen- 

 trations (see accompanying tabulation), and further alter the lipid compo- 



sition and increase fat desaturation. Phthiocol apparently acts somewhat 

 differently because, although it suppresses growth potently and reduces 

 the sterol content, it does not inhibit total lipid synthesis. In results like 

 this it is difficult to know if the lipid changes are due to direct action on 

 lipid metabolism or are secondary to growth depression. Maselli and Nord 

 (1952) believe that the naphthoquinones inhibit both the glucose utiliza- 

 tion and the metabolism of pyruvate to lipid; when acetate is present the 

 inhibitions are less. In yeast the picture is quite different, various quinones 

 either not effecting lipid synthesis or stimulating it somewhat, the stimu- 

 lation being mainly in the sterol fraction (Hoffmann-Ostenhof and Kriz, 

 1949 a, b). Even less is known about amino acid metabolism. p-Benzoqui- 

 none has been reported to accelerate the oxidative deamination of amino 

 acids in cress roots (Flaig and Reinemund, 1955), and jj-benzohydroquinone 

 reduces hair color, skin pigmentation, and melanin formation, presumably 

 blocking the oxidation of tyrosine (Denton et at., 1952). p-Benzoquinone 

 and 1,4-naphthoquinone markedly stimulate the "incorporation" of tyro- 

 sine-2-C^* into the proteins of liver homogenates (Kamin et al., 1957). 

 Actually it is not tyrosine but a melanin-like substance that is incorporated, 

 and much of the action is nonenzymic, occurring in the absence of the ho- 

 mogenate. Protein synthesis in Pseudomonas aeruginosa is quite potently 

 inhibited by both p-benzoquinone and p-benzohydroquinone, since the for- 

 mation of the adaptive enzyme for benzoate oxidation is depressed 76% by 

 0.09 mM (Bernheim, 1954). However, it is not known whether the site of 



