A novel approach for efficient immobilization and stabilization of papain on magnetic gold nanocomposites

In the present study, a facile functionalization of magnetic nanoparticles has been described for the immobilization of enzyme that offers many advantages for reuse and excellent efficiencies. The magnetic gold nanocomposites have been fabricated for the successful immobilization of an industrially important enzyme papain. For immobilization of papain on magnetic gold nanocomposites, magnetic nanoparticles were modified with 3-(mercaptopropyl) trimethoxysilane (MPTS). Further, the citrate stabilized gold nanoparticles were chemisorbed on these thiol coated magnetic nanoparticles to fabricate the desired magnetic gold nanocomposites. Papain containing net positive charge (isoelectric point of papain = 8.75) in PBS buffer (pH 7.4) has immobilized on the surface of the negatively charged magnetic gold nanocomposites through the ionic or electrostatic interaction. The Michaelis-Menten kinetic constant (K-m) and maximum reaction velocity (V-max) for free papain were 0.236 x 10(5)g ml(-1) and 4.08 g ml(-1)/s respectively whereas for immobilized papain, K-m and V-max values were 0.308 x 10(5)g ml(-1) and 5.4 g ml(-1)/s respectively. The loading amount of papain on magnetic gold nanocomposites was 54 mg/g support and the activity recovery of the immobilized papain reached to 47 (+/- 5)% compared to native papain. The main advantage of this papain nanobiocatalyst is the easy isolation of enzyme from the reaction medium. (C) 2012 Elsevier B.V. All rights reserved.