Immobilization of linamarase on non-porous glass beads

The immobilization of purified linamarase [beta-D-glucohydrolase, EC:3.2.1.21] onto non-porous glass beads involved the silanization of the HF-treated glass beads with 2% gamma-aminopropyl-triethoxysilane in acetone, covalent coupling of the alkyl amine to glutaraldehyde and subsequent attachment of the enzyme molecule to glutaraldehyde via a Schiff's base linkage. The immobilized linamarase catalyzed the hydrolysis of its natural substrate, linamarin (2-hydroxyisobutyro-nitrile-beta-D-glucopyranoside) and the synthetic substrate analog, p-nitrophenyl-beta-D-glucopyranoside (pNP-beta-D-glucopyranoside). Glucono-1,5-lactone inhibited the immobilized enzyme competitively irrespective of which of the two substrates was used, while imidazole showed competitive inhibition with linamarin as substrate but non-competitive inhibition with pNP-beta-D-glucopyranoside. The Ki values obtained for glucono-1,5-lactone were 2.04 mM and 0.97 mM with linamarin and pNP-beta-D-glucopyranoside as substrates, respectively. The Ki values for imidazole as inhibitor were 6.00 mM and 38.20 mM with these two substrates, respectively. The energies of activation, E-11, for the reaction catalyzed by the immobilized enzyme with linamarin and pNP-beta-D-glucopyranoside as substrates were 4.00 kcal/mol and 5.7 kcal/mol, respectively. Determination of the operational stability of the immobilized enzyme gave a half-life of 14 days at 27 degrees C assuming continual use of the immobilized enzyme in a fixed-bed reactor for the hydrolysis of cyanogenic glycosides. (C) 1998 Elsevier Science Ltd. All rights reserved.