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Articles

Partial Characterization of C_x Cellulase and Cellobiase from Ripening Tomato Fruits ¹

^a Department of Horticulture, University of Illinois, Urbana, Illinois 61801

Cellulolytic enzymes were studied in extracts from the locular contents of ripening fruits of Lycopersicon esculentum var. KC-146. When acting on carboxymethyl cellulose, the enzyme preparations were capable of decreasing the viscosity of the reaction mixture and generating reducing groups, oligosaccharides, and glucose. Cellobiose cellotriose, cellotetrose, and cellopentose also served as substrates for glucose production.

These properties were due to the presence in the extracts of two cellulolytic enzymes—C_x cellulase (E.C. 3.2.1.4) and cellobiase— (E.C. 3.2.1.21). No evidence was found for the presence of exocellulase or C₁, an enzyme which initiates enzymatic attack on insoluble cellulose.

Cellobiose was found to be weakly inhibitory to C_x cellulase. D-Glucono-1,5-lactone competitively inhibited cellobiase. The K_m for cellobiose was 0.34 mM, and the K_i for gluconolactone was 23 µM.

¹ This work was supported in part by National Science Foundation Grant GB 8764 and was conducted in part to fulfill the requirements of D. M. Pharr for a Ph.D. degree.

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