Purification and properties of an exo-(1-->3)-beta-D-galactanase from Aspergillus niger.
An exo-(1-->3)-beta-D-galactanase was purified by six chromatographic steps from a culture supernatant of Aspergillus niger. Its apparent molecular mass was 66 kDa, as estimated by SDS-PAGE analysis. The purified enzyme had no detectable activity on various p-nitrophenyl glycosides and on native plant polysaccharides but exhibited a high activity on a (1-->3)-beta-D-linked galactan backbone obtained after partial acid hydrolysis and two Smith degradations of gum arabic. The optimum conditions were pH 4.5 and 40-50 degrees C. The enzyme had a Michaelis constant (Km) of 1.9 mg/mL for the beta-(1-->3)-D-galactan with a maximum reaction velocity (Vmax) of 1380 nkat/mg. The study of the reaction products obtained after enzyme treatment of two galactans derived from gum arabic through one or two Smith degradations showed that it was an exo-(1-->3)-beta-D-galactanase able to by-pass the branching points of galactan backbones and thus to release the side-chains of type II arabinogalactans in an undegraded form.
Pellerin
P
P
Institut National de la Recherche Agronomique, Laboratoire des Polymères et des Techniques Physico-Chimiques, Montpellier, France.
Brillouet
J M
JM
D001234:Aspergillus niger / Q000201:enzymology*; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D004591:Electrophoresis, Polyacrylamide Gel; D005685:Galactans / Q000737:chemistry / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D013379:Substrate Specificity; D001616:beta-Galactosidase / Q000302:isolation & purification* / Q000378:metabolism*
D005685:Galactans; D006026:Glycoside Hydrolases; C063901:exo-beta-(1--3)-D-galactanase; D001616:beta-Galactosidase