Zeolite membranes to immobilize Catalase

Zeolite composite disk membranes provide an ideal support to immobilize enzymes for advanced applications such as membrane bioreactors, biosensors and disease diagnostics. In fact, they are composed of a zeolite selective film formed by inter-crystalline growth and, at the same time, they present a large number of zeolite crystals grown inside the meso-and macro-pores of inorganic support used in the hydrothermal synthesis [1]. Zeolite membranes have the advantage that the basic/acidic nature of the material can be modified by varying the Si/Al ratio or by introducing different metals (Me) into the crystalline framework. Furthermore, zeolite acidity can be adjusted by exchanging extra-framework metal cations with H+[2]. Finally, zeolite membranes are known to be stable both in wet and dry conditions then normally compatible with biochemical analyses. We recently reported the application of zeolite crystals and membranes as adsorbent materials for the immobilization of hard and soft proteins (BSA and cytochromec) and we observed that their amount adsorbed on zeolite materials increases when the zeolite crystals are inter-grown for forming a membrane [3], [4].

Here we report, the adsorption characteristics of catalase on different zeolite crystals synthesized in hydrothermal conditions. Catalase, present in the peroxisomes of nearly all aerobic cells, is a heme-containing metalloenzyme that is regarded as one of the most common enzymes in plant and animal tissues. It consists of four subunits, each of which contains a Fe3+ prosthetic heme group (protoporphyrin IX), which is exposed through a 26 Å long and 17 Å wide funnel shaped channel and is responsible for the its catalytic activity. This enzyme catalyzes the disproportion of hydrogen peroxide into water and oxygen (1): 2H O O +2H O (1) 2 2 2 2 Catalase has been used to eliminate of residual hydrogen peroxide in textile [5], food [6], semiconductor industries [7], and wastewater treatments [8], but the high cost of the enzyme has impeded its wide application. It is used in food technology [9] and was proposed as a therapeutic agent to be administered interperitoneally [10]. For these reasons and for its technological potentials, catalase was selected as model enzyme for this study. In all applications reported in the literature, catalase is largely preferred as immobilized enzyme, being more stable to proteolysis. Catalase films were immobilized by adsorption on a variety of polymeric surfaces such as carbon nanofibrous membranes [11], which were been studied using spectroscopic and electrochemical analyses. It was evident that major problems related to polymeric supports were been the inadequate resistance to extreme pH values of media, high temperatures, to bacterium presence, and degradation by proteolysis11 reaction. The novelty of the present work lies in the association of synthesis of zeolite membranes (which have superior physical-chemical characteristics such as thermal, pH and bacterial resistance) and the immobilization of enzyme. Zeolite materials were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (FESEM), ICP-MASS and single gas permeability. Owing to the high substrate surface area used, it was also possible to measure enzyme loss from the solution directly via UVspectroscopy. Catalytic tests were performed to verify the enzymatic activity after the adsorption on zeolite membranes.

The preparation of insoluble supports to adsorb enzymes is a primary aim of current research because immobilized enzymes possess several advantages over the free enzyme, for example an increase of biomolecule stability and the facility of its re-use and separation from the reaction media with spinoff in advanced applications in various fields such as biotechnology, bio-processing [12],[13], filtration, biosensors, diagnostic products, food manufacturing, cell culture, drug delivery, dentistry and medical engineering.