Enzymatic properties of α-galactosidase from Trichoderma reesei in the hydrolysis of galactooligosaccharides

Abstract Enzymatic properties of the α-galactosidase (α-galactoside galactohydrolase, EC 3.2.1.22) from Trichoderma reesei in the hydrolysis of natural galactooligosaccharides and α -O- methyl D-galactopyranoside have been investigated in a wide range of substrate concentrations. The hydrolyses of α -O- methyl D-galactopyranoside and melibiose were inhibited by substrate at concentrations higher than 100 mM while in the hydrolysis of raffinose and stachyose such an effect was not observed. It was shown by 1 H and 13 C NMR spectroscopy and HPLC techniques that inhibition by the excess of α -O- methyl D-galactopyranoside or melibiose strongly correlated with formation of transglycosylation products. The product of autocondensation reaction with α -O- methyl D-galactopyranoside as substrate was found to be α -O- methyl galactopyranosyl-1,6-D-galactopyranoside. The stereochemical course of stachyose hydrolysis has been determined. The enzyme catalyses the hydrolysis with retention of anomeric configuration and is assumed to operate via a double displacement mechanism. Simultaneous hydrolysis of stachyose and raffinose effected by the α-D-galactosidase was studied by direct 1 H NMR measurements. Cleavage of the terminal galactose residue of stachyose was found to be the rate-limiting step. Formation constants of enzyme-substrate complex for stachyose and raffinose were calculated. The suggested model can be used for simulating the two-substrate system and predicting the extent of stachyose hydrolysis.