174 CARBON METABOLISM III 



thought to he an intermediate (279). The process therefore resembles 

 the oxidation of substituted benzenes by bacteria (479) and higher 

 plants (313), in which benzoic acid is the ultimate product: 



CH 2 COOH CHO COOH 



I I I 



^\ ? fii rl (11) 



Phenylacetic acid Benzaldehyde Benzoic arid 



However, the entire sequence is not known in fungi, and the forma- 

 tion from phenylacetate of 2-hydroxyphenylacetate and 2,5-dihydroxy- 

 phenylacetate point to other possible modes of attack by fungi and 

 actinomycetes (297, 320, 544). Benzoic acid is formed in culture by 

 Penicillium roseo-purpureum (427a). 



The oxidation of vanillin and ferulic acid by fungi appears to be 

 of the same general type as that of phenylacetate, the side chain being 

 oxidized in one or more steps to a carboxyl group (268). 



There occurs in bacterial metabolism an oxidative fission of the 

 aromatic ring of catechol to yield m-m-muconic acid (480): 



OH 

 I OH 



+ 2 -> HOOC— CH=CH— CH=CH— COOH (12) 



Catechol CiJ-eir-muconic acid 



This over-all reaction has been hypothecated for Aspergillus niger 

 (57), and Penicillium sp. accumulates a's-cw-muconate during the oxi- 

 dation of catechol (333). The aromatic ring of phenylacetic acid is 

 split by Penicillium chrysogenum, but the details of the process are 

 not known, except that an induced enzyme system is responsible and 

 that compounds of the tricarboxylic acid cycle appear in the medium 

 during oxidation (294, 296). 



It has been mentioned that a mutant of Neurospora crassa accumu- 

 lates and then oxidizes protocatechuic acid. The ultimate product is 

 /3-ketoadipic acid and the enzymatic steps involved are similar to but 

 not identical with those known in Pseudomonas fluorescens (250, 481). 

 The first step is the conversion of procatechuic acid to cis, cis-fi-cax- 

 boxymuconic acid, analogously to the reaction of Equation 12, by an 

 inducible oxidase system (250, 251). 



The oxidation of phenols to quinones is a special problem, and 

 much more data are available on it than on other phases of aromatic 

 metabolism. 



