Characterization of a novel endopolygalacturonase fromAspergillus nigerwith unique kinetic properties

We isolated and characterized a new type of endopolygalacturonase (PG)‐encoding gene, pga D, from Aspergillus niger . The primary structure of PGD differs from that of other A. niger PGs by a 136 amino acid residues long N‐terminal extension. Biochemical analysis demonstrated extreme processive behavior of the enzyme on oligomers longer than five galacturonate units. Furthermore, PGD is the only A. niger PG capable of hydrolyzing di‐galacturonate. It is tentatively concluded that the enzyme is composed of four subsites. The physiological role of PGD is discussed.