Abstract
The present study investigated the carboxylation of silver nanoparticles (AgNPs) by 1: 3 nitric acid-sulfuric acid mixtures for immobilizing Aspergillus oryzae beta-galactosidase. Carboxylated AgNPs retained 93% enzyme upon immobilization and the enzyme did not leach out appreciably from the modified nanosupport in the presence of 100 mmol L-1 NaCl. Atomic force micrograph revealed the binding of beta-galactosidase on the modified AgNPs. The optimal pH for soluble and carboxylated AgNPs adsorbed beta-galactosidase (I beta G) was observed at pH 4.5 while the optimal operating temperature was broadened from 50 degrees C to 60 degrees C for I beta G. Michaelis constant, Km was increased two and a half fold for I beta G while Vmax decreases slightly as compared to soluble enzyme. beta-galactosidase immobilized on surface functionalized AgNPs retained 70% biocatalytic activity even at 4% galactose concentration as compared to enzyme in solution. Our study showed that I beta G produces greater amount of galacto-oligosaccharides at higher temperatures (50 degrees C and 60 degrees C) from 0.1 mol L-1 lactose solution at pH 4.5 as compared to previous reports.