Untersuchungen über den Abbaumechanismus einer gereinigten Polygalakturonase aus Aspergillus niger

Abstract

Using an Aspergillus niger enzyme preparation, a pure polygalacturonase has been isolated by chromatography on cellulose phosphate. The alkali‐labile enzyme has an isoelectric point of 4.5 and a pH optimum of 5.5; its activation energy is 8.3 kcal/mole. The enzyme hydrolyzes 48% of the glycosidic bonds in pectic acid. Besides di‐ and monogalacturonic acid, the hydrolysate mostly contains trigalacturonic acid. Depending on the degree of esterification, the methyl ester of pectic acid is degraded with varying intensity. If the degree of esterification exceeds 75%, pectin is no longer degraded. Acetylation of the secondary alcohol groups, up to 70%, has little effect. Di‐ and trigalacturonic acid are not hydrolyzed. Tetragalacturonic acid is split into mono‐and trigalacturonic acid, penta‐ and hexagalacturonic acid into tri‐, di‐ and monogalacturonic acid. The isolated enzyme is an endopolygalacturonase. The study of the degradation products strongly suggests that two carboxyl groups of pectic acid become attached to the binding sites of the enzyme molecule. These two groups are separated from the active center by three and six galacturonic acid units respectively. Blocking of the binding sites at higher substrate concentrations causes a decrease in enzyme activity.