The immobilization of enzymes on nylon structures and their use in automated analysis

Immobilization of thermolysin to polyamide nonwoven materials

In the last few years, an increasing number of biotechnological techniques have been applied to the restoration and conservation of works of art, paintings, old maps, and papers or books. Enzymes can solve problems that give restorers difficulties, although for many applications it is not possible to use soluble enzymes; therefore, it is necessary to look for suitable carriers for immobilization. Different methods for covalent immobilization of enzymes to polyamide nonwovens were tested, using thermolysin as an example. Two distinct strategies were pursued: (1). controlled, partial hydrolysis of the polymer and subsequent binding of the enzyme to the released amino and carboxy groups; and (2). attachment of reactive groups directly to the polyamide without disintegrating the polymeric structure (O-alkylation). Different spacers were used for covalent fixation of the enzyme in both cases. The enzyme was fixed to the released amino groups by glutaraldehyde, either with or without a spacer. Either way, active enzyme could be immobilized to the matrix. However, intense treatment caused severe damage to the stability of the nonwoven fabric, and reduced the mechanical strength. Conditions were investigated to conserve the nonwoven fabric structure while obtaining near-maximum immobilized enzyme activity. Immobilization of the enzyme to the released carboxy group after acid hydrolysis was performed using dicyclohexylcarbodiimide. In comparison to the enzyme bound via the amino group, the yield of immobilized enzyme activity was slightly lower when benzidine was taken as spacer and still lower with a 1,6-hexanediamine spacer. O-alkylation performed with dimethylsulfate caused severe damage to the nonwoven fabric structure. Considerably better results were obtained with triethyloxonium tetrafluoroborate. As the spacers 1,6-hexanediamine and adipic acid dihydrazide were used, activation for immobilizing thermolysin was performed with glutaraldehyde, adipimidate, and azide. With the exception of azide, all combinations of spacers and activation reagents gave high yields of immobilized enzyme activity. Thermolysin immobilized by this technique showed a remarkably improved stability with respect to elevated temperature, extreme pH values, and reduced polarity. The nonwoven fabric can be stored for weeks without loss of enzyme activity by washing with distilled water and drying.

Enzyme immobilization on nylon-optimization and the steps used to prevent enzyme leakage from the support

Because of its low cost, chemical and mechanical properties and ready availability in a number of different forms (e.g. powders, beads, nets, tubes, film, sheets, etc.) Nylon is an attractive matrix for enzyme immobilization. We report here a thorough evaluation of a protocol for enzyme immobilization on nylon film with relatively inexpensive and non-toxic reagents, involving acid hydrolysis, glutaraldehyde coupling and spacer molecules and employing beta-glucosidase and trypsin as model enzymes. We also describe steps for virtually eliminating enzyme leakage and non-specific binding. Individual steps in the procedure are simple and conditions flexible so, whilst evaluated in terms of binding proteins to nylon film, they should be applicable to other forms of nylon and suitable for binding most enzymes and proteins, including antibodies, providing a method having potential in both affinity chromatography/adsorption and in bioreactor applications.

Human serum albumin chromatography by Cibacron Blue F3GA-derived microporous polyamide hollow-fiber affinity membranes

An affinity dye ligand, Cibacron Blue F3GA was covalently attached onto commercially available microporous polyamide hollow-fibre membranes for human serum albumin (HSA) adsorption from both aqueous solutions and human plasma. Different amounts of Cibacron Blue F3GA were incorporated on the polyamide hollow-fibres by changing the dye attachment conditions, i.e. initial dye concentration, addition of sodium carbonate and sodium chloride. The maximum amount of Cibacron Blue F3GA attachment was obtained at 42.5 micromol g(-1) when the hollow-fibres were treated with 3 M HCI for 30 min before performing the dye attachment. HSA adsorption onto unmodified and Cibacron Blue F3GA-derived polyamide hollow-fibre membranes was investigated batchwise. The non-specific adsorption of HSA was very low (6.0 mg g(-1) hollow-fibre). Cibacron Blue F3GA attachment onto the hollow-fibres significantly increased the HSA adsorption (147 mg g(-1) hollow-fibre). The maximum HSA adsorption was observed at pH 5.0. Higher HSA adsorption was observed from human plasma (230 mg HSA g(-1) hollow-fibre). Desorption of HSA from Cibacron Blue F3GA derived hollow-fibres was obtained using 0. 1 M Tris-HCl buffer containing 0.5 M NaSCN or 1.0 M NaCl. High desorption ratios (up to 98% of the adsorbed HSA) were observed. It was possible to reuse Cibacron Blue F3GA derived polyamide hollow-fibre without significant decreases in the adsorption capacities.

Preparation of and optimal module housings for hollow fibre membrane ion exchangers

Macroporous polyamide 6 hollow fibres can be polymer coated by a three-step procedure: first, reaction of the amino end groups with a bifunctional, double-bond-containing reagent; second, block polymerization with different monomers; and third, polymer analogue reactions with amines or sulphite salts to produce ion exchanger groups. The densities of double bonds are dependent on the amino densities and are in the range of 20-30 mumol/g polyamide 6. The ion exchanger fibres were packed in different types of module housings to get an optimal separation unit. The best housing seems to be a so-called single-dead-end arrangement of fibres. Three types of ion exchanger hollow fibres have been produced: a weak and a strong anion exchanger and a strong cation exchanger. The dynamic protein-binding capacities are in the range of 40 mg/ml membrane. Using these membrane modules, it is possible to separate proteins in the same way as with particle-based ion exchangers. Fast protein separations with low pressure drop are possible.

Stability of immunoadsorbents comprising antibody fragments. Comparison of Fv fragments and single-chain Fv fragments

Immunoadsorbents comprising Fv fragments specific for hen egg lysozyme were used to recover the enzyme from a 20-fold excess of bovine albumin. We designed automatic equipment to run this model purification system for 100 cycles non-stop and monitored the deterioration of the immunoadsorbents during the cycling procedure. Only minor losses (approximately 25%) in the immunoadsorbents' capacity were detected; this correlated well with ligand loss (measured by enzyme-linked immunosorbent assay) which was approximately 0.2% per cycle. A surprising finding was that the use of "single-chain" Fv fragments conferred only a minor advantage with respect to stability of the immunoadsorbents.

Biosensors and flow injection analysis

Combining flow injection analysis with a biosensor is a novel biosensing process which has allowed speedy and accurate analysis. Diagnostic analysis is the most important application for biosensing flow injection analysis, but other applications include bioprocess monitoring, analysis of food and agricultural products, as well as environmental analysis. In addition, the analysis of compounds, such as explosives and abused drugs, and monitoring of Salmonella, the microorganism that causes food poisoning, have been reported.

Detoxification of organophosphate pesticides using a nylon based immobilized phosphotriesterase from Pseudomonas diminuta

A partially purified phophotriesterase was successfully immobilized onto nylon 6 and 66 membranes, nylon 11 powder, and nylon tubing. Up to 9000 U of enzyme activity was immobilized onto 2000 cm2 of a nylon 6 membrane where 1 U is the amount of enzyme necessary to catalyze the hydrolysis of 1.0 mumol of paraoxon/min at 25 degrees C. The nylon 66 membrane-bound phosphotriesterase was characterized kinetically where the apparent Km value for the immobilized enzyme was 0.35 mM. This is 5-6 times higher than that observed for the soluble enzyme. However, nylon immobilization limited the maximum rate of paraoxon hydrolysis to less than 10% of the value measured for the soluble enzyme. The addition of the cosolvent, methanol, resulted in an increase in the apparent Km value for paraoxon hydrolysis but concentrations up to 40% had no negative effect on the catalytic effectiveness with the soluble or immobilized phosphotriesterase. Based on the kinetic analysis, methanol appears to be a competitive inhibitor for both forms of enzyme. The nylon powder immobilized enzyme was shown to be stable for at least 20 mo. The immobilization of the phosphotriesterase onto nylon provides a practical method for the detoxification of organophosphate pesticides.

Use of immobilized enzymes in automated clinical analysis: determination of uric acid and glucose using immobilized enzymes in column form

We studied the use of immobilized enzymes, covalently bound to alkylaminosilane derivative of porous glass, to automated clinical analysis on uric acid and glucose in blood, serum and urine. A microcolumn with an immobilized enzyme was prepared and used in an AutoAnalyzer I continuous flow system. Uricase (EC 1.7.3.3) from Candida utilis and glucose oxidase (EC 1.1.3.4) from Aspergillus niger were immobilized for the determination of uric acid and glucose, respectively. Hydrogen peroxide produced by these oxidases was colorimetrically determined using horse-radish peroxidase (EC 1.11.1.7) and a hydrogen acceptor in solution. Sensitivity and wash charactertistics of a column with immobilized enzyme, 1.5 mm of inner diameter and up to 40 mm in length, were satisfactory at an assay speed of 50 samples per hour. The results correlated well with those obtained by other well established methods utilizing the AutoAnalyzer system. The immobilized enzymes were sufficiently stable for at least two months of 2000 tests when used repeatedly. Clinical trials proved that this method is capable of replacing the soluble enzyme method, giving reliable and reproducible results at lower cost.

Immobilized enzyme nylon tube reactors: creatininase and creatine kinase linked to the pyruvate kinase-lactate dehydrogenase indicator system in the detection of creatinine and creatine

A four enzyme system catalyzing a sequence of reactions was immobilized onto the inside surfaces of nylon tubes and studied as a possible method of analysis for the first substrate, creatinine in the sequence of reactions. The system was first studied in solution as a guide to optimizing conditions for preparation and use of the immobilized enzyme nylon tube reactors. The scope and limitations of this approach to routine analysis is discussed.

A method for enhancing the stability of thiol-containing enzymes immobilised on nylon

The limited stability of immobilised enzymes is a major factor restricting their use in clinical chemistry. The immobilisation procedure described here affords a simple method of enhancing the stability of certain enzymes immobilised on nylon. Studies with alcohol dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase have indicated that a significant increase in stability can be obtained using this immobilisation procedure as compared with conventional procedures. As anticipated the immobilisation procedure was unsatisfactory for oxidases such as glucose oxidase.

Immobilised monomers of human liver arginase

Human liver arginase (L-arginine amidinohydrolase, EC 3.5.3.1) was immobilised by attachment to nylon with glutaraldehyde as a crosslinking agent. Incubation of the immobilised tetrameric enzyme with EDTA followed by dialysis resulted in the dissociation of the enzyme into inactive matrix-bound and solubilised subunits. Both species recovered enzymatic activity after incubation with Mn2+, and the activity of the reactivated matrix-bound subunits was nearly 25% of that shown by the enzyme initially attached to the support in the tetrameric form. When the reactivated bound subunits were incubated with soluble subunits in the presence of Mn2+, they 'picked-up' from the solution an amount of protein and enzymatic activity almost identical to that initially lost by the immobilised tetramer after the dissociating treatment with EDTA. This occurred only in the presence of Mn2+. It is suggested that the reactivation of the subunits of arginase involves the initial formation of an active monomer, which then acquires a conformation that favours a reassociation to the tetrameric state.

Hydrolysis of D-galactosides in an open tubular lactase reactor

Lactase (beta-galactosidase) was attached to the inner surface of nylon tubing. Tubes of various lengths were used to bring about the hydrolysis of o-nitrophenyl-beta-D-galactoside and of lactose in skim milk. The results with the former substrate were analyzed in the light of a theoretical treatment of Kobayashi and Laidler (Biotechnol. Bioeng., 16, 99, 1974), with the conclusion that the reaction is intermediate between diffusion-free and completely diffusion-controlled behavior. The results with skim milk show that with a single 46 m tube and continuous circulation, 90% of the lactose is removed within 20 hr. A battery of ten such tubes, with single passage, at a flow rate of 2 cm/sec, would remove more than 99% of the lactose in less than 40 min.