Mechanisms of Cellulases and Xylanases: A Detailed Kinetic Study of the Exo-.beta.-1,4-glycanase from Cellulomonas Fimi

• Published in: Biochemistry (Easton) Vol. 33; no. 20; pp. 6363 - 6370
• Main Authors: Tull, Dedreia, Withers, Stephen G
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 01.05.1994
• Subjects: Actinomycetales - enzymology; ACTIVIDAD ENZIMATICA; ACTIVITE ENZYMATIQUE; BACTERIA; beta-Glucosidase - metabolism; Cellobiose - analogs & derivatives; Cellobiose - metabolism; Cellulomonas fimi; Deuterium; Enzyme Activation; Enzyme Reactivators; GLICOSIDOS; Glucan 1,4-beta-Glucosidase; GLUCOSIDE; GLUCOSIDOS; GLYCOSIDE; HIDROLASAS; Hydrogen-Ion Concentration; HYDROLASE; Kinetics; Substrate Specificity
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi00186a041

The exoglucanase/xylanase from Cellulomonas fimi (Cex) has been subjected to a detailed kinetic investigation with a range of aryl beta-D-glycoside substrates. This enzyme hydrolyzes its substrates with net retention of anomeric configuration, and thus it presumably follows a double-displacement mechanism. Values of k(cat) are found to be invariant with pH whereas kc(cat)/K(m) is dependent upon two ionizations of pK(a) = 4.1 and 7.7. The substrate preference of the enzyme increases in the order glucosides cellobiosides xylobiosides, and kinetic studies with a range of aryl glucosides and cellobiosides have allowed construction of Broensted relationships for these substrate types. A strong dependence of both k(cat) [beta(1g)