IK', CARBON METABOLISM II 



The indefinite nature of the substrate, the crudity of the enzyme 

 assay, and the fact that other enzymes may solubilize the pectic 

 materials of plants (116) are compelling reasons to doubt the real 

 existence of protopectinase. This doubt is reinforced by the finding 

 (102) that a partially purified pectin-polygalacturonase from Byssoch- 

 lamys fulva causes disintegration of tobacco tissue. Although it is 

 possible, of course, that the preparation was contaminated with a 

 protopectinase, it seems more probable that pectin-polygalacturonase 

 has the ability, usually ascribed to protopectinase, to macerate tissue. 

 It is significant in this connection that all protopectinase preparations 

 examined contain pectin-polygalacturonase (115). 



The present nomenclature of the pectic enzymes was first clearly 

 formulated in 1927 (61) and fully worked out only in 1914 (117). 

 Consequently the earlier work on these enzymes employs different and 

 often highly individual nomenclature. In particular, the "pectinase" 

 of the older literature is usually synonymous with what is now called 

 protopectinase, i.e., the tissue-macerating enzyme. Pectinase as now 

 understood is a synonym for pectin-polygalacturonase. The nomencla- 

 ture used here is that of Kertesz (116). 



The pectinic acids are colloidal macromolecules composed of a-D- 

 anhydrogalacturonic acid units linked together through 1 ,4-a-glycosidic 

 bonds. The carboxyl groups of some of the galacturonic acid residues 

 are esterified with methyl alcohol. Certain pectinic acids of specific 

 properties are designated pectins. Pectinic acids are obtained from 

 the crude plant pectic materials by partial hydrolysis. 



Excluding protopectinase from consideration, the known and 

 postulated pectic enzymes of fungi are of three types, depending on 

 their action on pectinic acids. They are: 



1. Pcctin-methylesterase, catalyzing the hydrolysis of the methyl 

 ester groups of pectinic acids, and converting pectinic acids to pectic 

 acids (polygalacturonic acids). 



2. Pectin-polygalacturonase, hydrolyzing the pectic acids to free 

 D-galacturonic acid. 



3. Pectin-depolymerase, a less well-known enzyme thought to cause 

 a partial hydrolysis of pectic acids to smaller units without the ap- 

 pearance of free galacturonic acid. 



Pectin-methylesterase (pectase, pectinesterase, pectinmethoxylase) 

 was originally denned (61) as an enzyme converting soluble pectin 

 (pectinic acid) into insoluble calcium pectate. Its action may be 

 schematized as: 



(R— CO— O— CH 3 )„ + (n)H 2 -» (R— COOH),, + (w)CH 3 OH (6) 



