Study on the role of tyrosine side-chains at the active centre of emulsin beta-D-glucosidase

• Published in: Biochimica et biophysica acta Vol. 662; no. 2; p. 308
• Main Authors: Kiss, L, Kóródi, I, Nańasi, P
• Format: Journal Article
• Language: English
• Published: Netherlands 15-12-1981
• Subjects: Acetylation; beta-Glucosidase - metabolism; Glucosidases - metabolism; Imidazoles - pharmacology; Kinetics; Seeds - enzymology; Sulfhydryl Reagents - pharmacology; Tyrosine
• ISSN: 0006-3002
• DOI: 10.1016/0005-2744(81)90043-7

The role of exposed tyrosine side-chains in enzyme-catalyzed reaction by sweet almond emulsin beta-D-glucosidase (beta-D-glucoside glucohydrolase, EC 3.2.1.21) has been studied using N-acetylimidazole as the specific reagent. The changes in activity, binding affinity and kinetic parameters (Km, V) as a result of acetylation of the phenolic hydroxyl groups have been determined. The acetylation increased the Km values of both beta-glucosidase and beta-galactosidase activities, whereas V remained unchanged. Similarly, the binding affinity for immobilized phenyl beta-D-glucopyranoside decreased appreciably. After the removal of the acetyl groups the enzyme regained 96% of the original activity. It is concluded that the tyrosine moieties, located in the active centre of the enzyme, have both glucoside and galactoside binding functions.