POLYSACCHARIDES 



117 



The enzyme occurs in commercial enzyme preparations of pectin- 

 polygalacturonase (75) and in the fungi listed in Table 3. The 

 enzyme of Fusarium oxysporum var. lycopersici appears to differ from 

 that of commercial preparations from other fungi (241), and the latter 

 in turn differs from the pectin-methylesterase of higher plants (145). 



Production of extracellular pectin-methylesterase by Botrytis cinerea 

 and Aspergillus niger occurs if pectin is the growth medium but only 

 to a negligible degree with glucose as the carbon source (3, 80, 81). 

 The extracellular enzyme of Penicillium chrysogenum is formed only 

 if pectin, pectic acid, or chemically related substances are in the 

 growth medium (176). Recently, the role of pectin-methylesterase in 

 the pathogenicity of fungi to plants has received attention. 



The third major category of the pectic substances is that of the 

 pectic acids, derived from pectinic acids by de-esterification. They 

 are colloidal polygalacturonic acids with molecular weights ranging 

 from 25,000 to 100,000. The molecule consists of D-galacturonic acid 

 units and may be visualized as follows: 



coo- 



coo- 



coo- 



The enzyme hydrolyzing the pectic acids has been named variously 

 pectinase, pectolase, and polygalacturonase. The most unambiguous 

 name appears to be pectin-polygalacturonase (116). It acts on the 

 de-esterified portions of pectinic acids or on the pectic acids resulting 

 from complete de-esterification of pectinic acids. It is often con- 

 taminated with pectin-methylesterase, and the mixture of the two 

 enzymes will, of course, act on pectinic acids both by de-esterification 

 and by hydrolysis. The product of pectin-polygalacturonase activity 

 on a polygalacturonide is, eventually, free D-galacturonic acid. The 

 properties of the enzyme have been studied extensively by Matus (144). 



Table 3 lists the fungi which have been shown to form the enzyme, 

 as assayed on pectinic acid or polygalacturonic acids, i.e., excluding 

 assays of tissue-macerating enzyme. Two comments are apposite to 

 the problem of the occurrence of the enzyme in fungi. First, it is 

 probable that the fungi producing protopectinase always form pectin- 

 polygalacturonase or that the two enzymes are identical. If either of 

 these hypotheses is true, then the sources of protopectinase given in 

 Table 3 must be included, adding numerous phycomycetes and 



