Effect of protease digestion on the activity of sugardepleted enzymes prepared with endo-β-N-acetylglucosaminidase from Flavobacterium sp

Endo-β-N-acetylglucosaminidase, purified to homogeneity from the culture filtrate of a Flavobacterium sp., liberated the carbohydrate chains from yeast invertase. About 90% of the carbohydrate associated with this glycoprotein was removed by the endo-β-N-acetylglucosaminidase. The native and carbohydrate-depleted enzymes were compared and found to exhibit similar catalytic activities, thermal stabilities and pH-activity profiles. However, the carbohydrate-depleted invertase was more susceptible to proteases with relatively broad specificities such as subtilisin and pronase, as found on examination of the enzyme activity and electrophoresis. On the other hand, trypsin did not have such an effect on the enzyme activities of the native and carbohydrate-depleted enzymes. The endo-β-N-acetylglucosaminidase also released carbohydrate chains from the purified β-N-acetylhexosaminidase of Penicillium oxalicum. Although the native and carbohydrate-depleted β-N-acetylhexosaminidases did not differ significantly in their stabilities or pH-activity profiles, the carbohydrate-depleted form was more susceptible to proteolysis by subtilisin, pronase and trypsin. From these results, it would appear that the carbohydrate of a glycosylated enzyme plays a role in protecting the enzyme from proteolysis.