Preparation and Characterization of Cross-Linked Pei-Lipase Aggregates With Improved Activity and Stability

Abstract

Using polyethyleneimine (PEI) as the sole precipitation and aggregation agent, PEI-enzyme complexation was investigated with lipases from Rhizomucor miehei, Thermomyces lanuginosus and Candida antarctica. The approach relied on rapid development of PEI-lipase aggregates in a solution and followed by glutaraldehyde cross-linking thus resulting in cross-linked PEI-lipase aggregates. PEI to enzyme mass ratio of a 1/ 20-40 range, alkaline pH and the absence of impurities produced higher coupling yields and activities. The pH affected the precipitatibility and/or relative activity of the aggregates. Impurities in some lipase preparations may prevent the formation or precipitation of the PEI-lipase aggregates. The aggregates attained higher stabilities especially at high pHs and enhanced thermostability with at least a 20-fold at ambient temperatures. By using p-nitrophenyl propionate as a soluble substrate, app. Vmax for the immobilized lipase increased by two-fold with only 25% increment in app. Km compared with the soluble lipase. Complexation with PEI may have produced favorable interface assisting for conformational change for the lipase activation. Thus, cross-linked PEI-lipase aggregates with ease of recovery and stability can be simple and inexpensive alternative for carrier-free immobilized lipases.