176 CARBON METABOLISM III 



Polyphenol oxidases in the fungi are often present only at particular 

 times in the culture cycle, especially during autolysis (188, 500), or only 

 in particular morphological structures (342, 344). The medium used 

 affects the production of the enzymes, both positively and negatively. 

 Laccase formation by Polyporus versicolor is increased non-specifically 

 by constituents of the medium and specifically by certain aromatic 

 compounds which probably act as inducers (189, 190). Both carbon 

 source and growth temperature affect enzyme synthesis in Glomerella 

 cingulata (499). Negative effects of an interesting type have been 

 found in studies on Neurospora crassa (287): in a medium containing 

 the usual level of sulfate a sulfur-containing dialyzable tyrosinase in- 

 hibitor is formed, the result being that the conventional assay detects 

 tyrosinase only in cultures grown in a low-sulfate medium. This 

 finding requires that earlier negative reports be re-evaluated. 



The tannins are esters of polyhydroxy phenols with aromatic acids, 

 and are hydrolyzed by tannase, e.g., 



HO HO OH HO 



-CO— O— C /> -» 2HO— i 



HO COOH HO 



Digallic acid Gallic acid 



The enzyme, an esterase, also hydrolyzes other similar esters (498). 

 The tannase of Aspergillus niger is inducible (322); its properties and 

 purification are summarized by Dyckerhoff and Armbruster (175), 

 and partial purification has been reported (519). Although most 

 studies have been made on the tannase of A. niger, the enzyme has 

 been reported in a few other fungi (36, 448, 574). 



The Significance of Aromatic Compounds. Some of the aromatic 

 compounds bulk rather large in the economy of the organism, amount- 

 ing to an appreciable fraction of the glucose consumed (140) and of 

 the dry weight produced (128). Those which have been studied in 

 relation to the history of the culture appear to be first formed and 

 then utilized (93, 95), to be more than inactive waste products of 

 metabolism. 



Possibly the most likely metabolic significance of these compounds 

 is as products of an unbalanced nutrition and metabolism. Most of 

 them have been isolated from fungi grown on media very high in 

 carbon; thus, the glucose Czapek-Dox medium often used has a car- 

 bon : nitrogen ratio of 60. Under these conditions, it is not surprising 



