Stereochemistry of the hydrolysis reaction catalyzed by endoglucanase Z from Erwinia chrysanthemi

Abstract

Endoglucanase Z from the phytopathogenic bacterium Erwinia chrysanthemi (strain 3937) was purified by affinity chromatography on microcrystalline cellulose Avicel PH101. A kinetic characterization using p-nitrophenyl β-d-cellobioside and p-nitrophenyl β-d-lactoside as substrates was conducted: endoglucanase Z exhibited K _m values of 3 mM and 7.5 mM and V _m values of 129 and 40 nmol·min⁻¹·mg⁻¹ towards p-nitrophenyl β-d-cellobioside (k _cat=0.1 s⁻¹) and p-nitrophenyl β-d-lactoside (k _cat=0.03 s⁻¹), respectively). The hydrolysis of cellotetraitol by endoglucanase Z was followed by HPLC and ¹H NMR. Results show that cellobiitol and β-cellobiose are initially formed, demonstrating that the enzyme is acting by a molecular mechanism retaining the anomeric configuration. This suggests the involvement of a glycosyl-enzyme intermediate.