Hydrolytic Activity and Substrate Specificity of an Endoglucanase from Zea mays Seedling Cell Walls.
An endoglucanase was isolated from cell walls of Zea mays seedlings. Characterization of the hydrolytic activity of this glucanase using model substrates indicated a high specificity for molecules containing intramolecular (1-->3),(1-->4)-beta-d-glucosyl sequences. Substrates with (1-->4)-beta-glucosyl linkages, such as carboxymethylcellulose and xyloglucan were, degraded to a limited extent by the enzyme, whereas (1-->3)-beta-glucans such as laminarin were not hydrolyzed. When (1-->3),(1-->4)-beta-d-glucan from Avena endosperm was used as a model substrate a rapid decrease in vicosity was observed concomitant with the formation of a glucosyl polymer (molecular weight of 1-1.5 x 10(4)). Activity against a water soluble (1-->3),(1-->4)-beta-d-glucan extracted from Zea seedling cell walls revealed the same depolymerization pattern. The size of the limit products would indicate that a unique recognition site exists at regular intervals within the (1-->3),(1-->4)-beta-d-glucan molecule. Unique oligosaccharides isolated from the Zea (1-->3),(1-->4)-beta-d-glucan that contained blocks of (1-->4) linkages and/or more than a single contiguous (1-->3) linkage were hydrolyzed by the endoglucanase. The unique regions of the (1-->3),(1-->4)-beta-d-glucan may be the recognition-hydrolytic site of the Zea endoglucanase.
Hatfield
R D
RD
Botany Department, Iowa State University, Ames, Iowa 50011.
Nevins
D J
DJ