233 



Quinones 



metabolism, and arise in a manner analogous to the accumula- 

 tion of citric acid, which is induced under the same conditions.^ 



There is no convincing experimental evidence that anthra- 

 quinones are important in electron transport. 



It has been suggested^" that anthraquinones are acetate-de- 

 rived, and there is some experimental confirmation.^^' ^^' * 



This proof was obtained by growing the mold in the presence 

 of C'*-labeled acetate, isolating the metabolite, which incorpo- 

 rated the label to some degree, then degrading the molecule by 

 ingenious chemical methods to determine the sites of labeling. 



Although an acetate origin is indicated, the detailed natures 

 of the intermediates in the biosynthetic mechanism are still 

 unknown. Intermediates such as orselHnic acid,^^ dihydroxy- 

 phthalic acid,^* and 6-methylsalicylic acid^^ (all known mold 

 metabolites) have been proposed, e.g.: 



COOH 



COOH 



3,5-Dihydroxy- 

 phthalic Acid 



COOH 



6-Methylsali 

 cylic Acid 



Birch prefers to think in terms of an intermediate formally 

 resembling a polyketomethylene chain, which can be modified 

 in various ways on an enzyme surface to yield related metabo- 

 lites. This concept is supported by the occasional discovery of 

 related metabolites in the same culture or plant. For example, 

 the co-occurring anthraquinone and phenanthrenequinone 



9 H. A. Krebs, Biochem. J. 31 2095 (1937). 



"A. J. Birch and F. W. Donovan, Austral. J. Chem. 6 360 (1953). 



" Sten Gatenbeck, Acta Chem. Scand. 12 1211 (1958). 



12 A. J. Birch, A. J. Ryan and Herchel Smith, /. Chem. Soc, 4473 

 (1958). 



* Also see addendum for later work. 



1^ K. Aghoramurthy and T. R. Seshadrl, J. Sci. Ind. Res. (India) 

 13A 114 (1959). 



"E. L. Tatum, Ann. Rev. Biochem. 13 667 (1944). 



15 Harold Raistrick, Acta Chem. Fenn. lOA 237 (1950). 



