118 CARBON METABOLISM II 



basidiomycetes to a list which is predominantly composed of ascomy- 

 cetes and imperfect fungi. Second, the fact that many fungi form 

 pectin-polygalacturonase only if pectinic acids or related materials are 

 present in the medium means that a complete survey of representative 

 fungi should use such a medium; in addition, in any such survey the 

 pH of the medium should be kept below 6.0 by reason of the rapid 

 inactivation of the enzyme at higher pH values (116). From the data 

 available and in the light of these considerations, it seems likely that 

 most fungi are able, at least under favorable conditions, to elaborate 

 pectin-polygalacturonase. 



The pectin-polygalacturonase of fungi differs in its properties from 

 the corresponding enzymes of yeast and higher plants (118, 133). The 

 enzyme is highly specific to pectic acids, failing to hydrolyze other 

 galacturonides or other uronides (131). Separation from pectin- 

 methylesterase has been accomplished (131, 136). It is not yet possible 

 to assert that pectin-polygalacturonase is a single enzymatic entity. 

 One view (114) is that it is a single enzyme acting by random scission 

 of the pectic acid molecule to form shorter galacturonic acid chains 

 and eventually free galacturonic acid. On the other hand, it has 

 recently been suggested that three different enzymes are involved in 

 Aspergillus foetidus (6, 63). 



The pectin-polygalacturonase of Penicillium chrysogenum and of 

 Fusarium spp. appears to be elaborated adaptively, in media with 

 pectin as carbon source but not in glucose media (47, 176), but the 

 same enzyme in other fungi is formed in glucose media (64, 80, 81). 

 All these experiments were carried out by growing cells from a spore 

 inoculum in media with or without the presumed inducing substrate; 

 hence, a possible effect of mutation or selection was not rigorously 

 excluded. 



Other enzymes, depolymerases, acting on pectins have been described 

 in plant parasitic and saprophytic fungi (17, 19a, 88, 195, 209). These 

 enzymes share in common the characteristic that only certain of the 

 glycosidic linkages of the substrate are attacked, resulting in the 

 liberation of short-chain polyuronides. The existence of such enzymes 

 in fungi has been challenged (192, 197), but the evidence, especially 

 that from work on Neurospora crassa (195) is strong. 



Assay methods for the pectic enzymes are reviewed by Kertesz (116); 

 cup plate assays have been devised (53) and may be particularly useful 

 in survey studies. There is some doubt (116) that assay of pectin- 

 methylesterase by hydrolysis of the half calcium salt of methyl-D- 

 tartaric acid (157) is valid. 



It seems that the immediate problem in the study of the pectic 



