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Articles

-D-Glucan Hydrolase Activity in Zea Coleoptile Cell Walls ^1,2

Department of Botany, Iowa State University, Ames, Iowa 50011

Enzymes dissociated from corn (hybrid B73 x Mo17) seedling cell walls by solutions of high ionic strength possess the capacity to degrade Avena caryopsis glucan. Inhibitor studies disclosed that both endo- and exoenzyme activities were involved and that the reaction sequence paralleled the autolytic solubilization of -D-glucan in isolated cell walls.

The salt-dissociated exoenzyme activity was strongly inhibited by HgCl₂ and to a lesser extent by parachloromercuribenzoate at a concentration of 100 micromolar. In the absence of these inhibitors, Avena caryopsis glucan was converted to monosaccharide, whereas in the presence of the mercurials, only endoenzyme activity was apparent and the glucan substrate was hydrolyzed yielding products with an average molecular size of 1.5 to 3.0 x 10⁴ daltons. Endoenzyme hydrolysis of the caryopsis glucan could not be attributed to the participation of an enzyme specific for mixed-linkage substrates.

The autolytic capacity of isolated cell walls was similarly affected by inhibitors. In the presence of 100 micromolar HgCl₂, cell walls released from 60 to 80 micrograms per milligram dry weight as polymeric glucan during a 24-hour period. Monosaccharide accounted for less than 2% of the autolytically solubilized products. Analysis of the polymeric glucan product revealed a similarity in molecular size to the products obtained following treatment of Avena caryopsis glucan with salt-dissociated wall protein. The results suggest that among the salt-dissociated proteins are those responsible for the autolytic capacity of isolated cell walls.

² These results were presented in part as papers entitled "Autolysis in isolated corn cell walls: role of a sulfhydryl protein" and "-D-glucan in corn coleoptile cell walls: evidence for linkage irregularity" at the national meeting of the American Society of Plant Physiologists held at Ohio State University in August, 1979.

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