Hs. Kelkar et Mv. Deshpande, PURIFICATION AND CHARACTERIZATION OF A PULLULAN-HYDROLYZING GLUCOAMYLASE FROM SCLEROTIUM-ROLFSII, Starke, 45(10), 1993, pp. 361-368
The pullulan-hydrolyzing enzyme from the culture filtrates of Scleroti
um rolfsii grown on soluble starch as a carbon source has been purifie
d by ultrafiltration (Amicon, PM-10), ion-exchange chromatography (DEA
E-Cellulose DE-52) and gel filtration chromatography (Bio-Gel P-150).
The enzyme moved as a single band in non-denaturing polyacrylamide gel
electrophoresis carried out at pH 2.9 and 7.5. The relative molecular
mass of the enzyme was estimated to be 64.000 D by SDS-PAGE and 66.07
0 D by gel filtration on Bio-Gel P150. The enzyme hydrolyzed pullulan
optimally at 50-degrees-C between pH 4.0-4.5, whereas, soluble starch
was optimally hydrolyzed at a pH of between 4.0-4.5 and at 65-degrees-
C. The Michaelis constant (Km) for pullulan was 5.13 mg . ml-1 (V(max)
1.0 U . mg-1) and for soluble starch, it was 0.6mg . ml-1 (V(max) 8.3
3 U . mg-1). The enzyme was observed to be a glycoprotein (12-13% carb
ohydrate by weight) and had a strong affinity for Concanavalin A. The
enzyme hydrolyzed alpha-D-glucans in an exo-manner, which resulted in
the release of glucose as the sole product of hydrolysis. Acarbose, a
maltotetraose analog, was found to be a potent inhibitor of both pullu
lan and starch hydrolysis (100% inhibition at 0.06 muM). The enzyme ha
s been characterized as a glucoamylase (1,4-alpha-D-glucan glucohydrol
ase, EC 3.2.1.3) showing a significant action on pullulan.