Development of an immobilized brain glutamine synthetase liquid chromatographic stationary phase for on-line biochemical studies

Biocatalysts: Measurement, modelling and design of heterogeneity

Multiple phenomena are involved in conversions by immobilized biocatalysts. A paradox is identified between analytical desires on one hand and analytical boundary conditions on the other: while the study of interdependent phenomena would call for their simultaneous analysis in an integrated context, the available experimental options may impose a series of separate and dedicated analyses. From this analysis, bottlenecks in particle performance may be identified, if possible supported by a mechanistic model and performance criteria. Subsequently, a strategy for further biocatalyst development may be chosen. Finally, possibilities for future improvement of biocatalysts are discussed for various fields of research. Some examples of recent developments in enzyme and matrix characteristics, reactor operation, and micro-technology are discussed.

Development and characterization of an immobilized enzyme reactor (IMER) based on human glyceraldehyde-3-phosphate dehydrogenase for on-line enzymatic studies

Immobilized enzyme reactors (IMERs) for on-line enzymatic studies are useful tool to select specific inhibitors and may be used for direct determination of drug-receptor binding interactions and for the rapid on-line screening to identify specific inhibitors. This technique has been shown to increase the stability of enzymes. The enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) plays an important role in the life cycle of the Trypanosoma cruzi and it has become a key target in the drug discovery program for Chagas' disease. Crystallographic studies have indicated that there are significant inter-species differences in GAPDH activity and sensitivity. For example the active sites of GAPDH in T. cruzi and humans differ by a substitution of ASP(210) (T. cruzi) by Leu(194) in human. Based on this information we initiated the study to develop optimal conditions for the covalent immobilization of the human GAPDH enzyme on a modified capillary support (400 mm x 0.10 mm). The chromatographic separation of NAD from NADH was achieved using a RP-Spherex-diol-OH (10 cm x 0.46 cm, 10 microm, 100 A) column. By using multidimensional HPLC chromatography system it was possible to investigate the activity and kinetic parameters of the GAPDH-IMER. The values obtained for D-GA3P and NAD were K(m)=3.5+/-0.2 mM and 0.75+/-0.04 mM, respectively, and were compared with values obtained with the free enzyme. The activity of the immobilized GAPDH has been preserved for over 120 days.

The covalent immobilization of microsomal uridine diphospho-glucuronosyltransferase (UDPGT): initial synthesis and characterization of an UDPGT immobilized enzyme reactor for the on-line study of glucuronidation

The microsomal fraction of rat liver containing uridine diphospho-glucuronosyltransferase (UDPGT; EC 2.4.1.17) has been covalently immobilized on a high performance chromatographic support. In this study Nucleosil Si-500 silica was converted into diol-bonded silica and subsequently converted into an aldehyde form through oxidation with sodium periodate. The microsomal fraction was immobilized via Schiff base formation followed by reduction with sodium cyanoborohydride. The resulting immobilized enzyme reactor (IMER) was placed in a multi-dimensional chromatographic system which utilized a mixed mode (C18 and anion exchange) column to trap the parent compound and glucuronide and a C18 column to separate the substrate and product. The IMER system was used for the online glucuronidation of 4-methylumbelliferone (4Me7OHC) and acetaminophen (APAP). The Michaelis-Menten kinetic parameters (Km and Vmax) associated with the formation of 4Me7OHC and APAP glucuronides demonstrated that the immobilization had not significantly affected the enzymatic activity of the UDPGT relative to the non-immobilized enzyme. The IMER retained enzymatic activity for more than 6 weeks. The results of this study demonstrate an easy and convenient way to identify compounds which may be glucuronidated and to synthesize and characterize the resulting products.

Application of immobilized enzyme reactor in on-line high performance liquid chromatography: A review

This review summarizes all the research efforts in the last decade (1994-2003) that have been spent to the various application of immobilized enzyme reactor (IMER) in on-line high performance liquid chromatography (HPLC). All immobilization procedures including supports, kind of assembly into chromatographic system and methods are described. The effect of immobilization on enzymatic properties and stability of biocatalysts is considered. A brief survey of the main applications of IMER both as pre-column, post-column or column in the chemical, pharmaceutical, clinical and commodities fields is also reported.

Immobilized enzyme reactors based upon the flavoenzymes monoamine oxidase A and B

Monoamine oxidase (MAO) catalyzes the oxidative deamination of amines. The enzyme exists in two forms, MAO-A and MAO-B, which differ in substrate specificity and sensitivity to various inhibitors. Membrane fractions containing either expressed MAO-A or MAO-B have been non-covalently immobilized in the hydrophobic interface of an immobilized artificial membrane (IAM) liquid chromatographic stationary phase. The MAO-containing stationary phases were packed into glass columns to create on-line immobilized enzyme reactors (IMERs) that retained the enzymatic activity of the MAO. The resulting MAO-IMERs were coupled through a switching valve to analytical high performance liquid chromatographic columns. The multi-dimensional chromatographic system was used to characterize the MAO-A (MAO-A-IMER) and MAO-B (MAO-B-IMER) forms of the enzyme including the enzyme kinetic constants associated with enzyme/substrate and enzyme/inhibitor interactions as well as the determination of IC(50) values. The results of the study demonstrate that the MAO-A-IMER and the MAO-B-IMER can be used for the on-line screening of substances for MAO-A and MAO-B substrate/inhibitor properties.

Monolithic micro-immobilized-enzyme reactor with human recombinant acetylcholinesterase for on-line inhibition studies

The development and characterization of a human recombinant acetylcholinesterase (hrAChE) micro-immobilized-enzyme reactor (IMER), prepared by using an in situ immobilization procedure is reported. hrAChE was covalently immobilized on an ethylenediamine (EDA) monolithic convective interaction media (CIM) disk (12 mm x 3 mm i.d.), previously derivatized with glutaraldehyde. The optimal conditions for the immobilization were: 12 microg of enzyme dissolved in 800 microl of phosphate buffer (50 mM, pH 6.0). The mixture was gently agitated overnight at 4 degrees C. The resulting Schiff bases were reduced by cyanoborohydride and the remaining aldehydic groups were condensed with monoethanolamine. Under these conditions, 0.22 U of hrAChE were immobilized with retention of 3.0% of the initial enzymatic activity. The activity of the immobilized hrAChE was stable for over 60 days. The activity and kinetic parameters of the hrAChE micro-IMER were investigated by inserting the micro-IMER in a HPLC system and it was demonstrated that the enzyme retained its activity. The micro-IMER was characterized in terms of units of immobilized enzyme and best conditions for immobilization yield. IMERs were compared for their relative enzyme stability, immobilized units, yield and aspecific matrix interactions. The effect of AChE inhibitors was evaluated by the simultaneous injection of each inhibitor with the substrate. The relative IC50 values were found in agreement with those derived by the conventional kinetic spectrophotometric method. In comparison with previously developed AChE-based IMERs, AChE monolithic micro-IMER showed advantages in terms of reduction of analysis time (2 min), lower aspecific matrix interactions and lower backpressure. Included in a HPLC system, it can be used for the rapid screening of new compounds' inhibitory potency. The advantages over the conventional methods are the increased enzyme stability and system automation which allows a large number of compounds to be analyzed in continuous.

Drug affinity to immobilized target bio-polymers by high-performance liquid chromatography and capillary electrophoresis

This review addresses the use of high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE) as affinity separation methods to characterise drugs or potential drugs-bio-polymer interactions. Targets for the development of new drugs such as enzymes (IMERs), receptors, and membrane proteins were immobilized on solid supports. After the insertion in the HPLC system, these immobilized bio-polymers were used for the determination of binding constants of specific ligands, substrates and inhibitors of pharmaceutical interest, by frontal analyses and zonal elution methods. The most used bio-polymer immobilization techniques and methods for assessing the amount of active immobilized protein are reported. Examples of increased stability of immobilized enzymes with reduced amount of used protein were shown and the advantages in terms of recovery for reuse, reproducibility and on-line high-throughput screening for potential ligands are evidenced. Dealing with the acquisition of relevant pharmacokinetic data, examples concerning human serum albumin binding studies are reviewed. In particular, papers are reported in which the serum carrier has been studied to monitor the enantioselective binding of chiral drugs and the mutual interaction between co-administered drugs by CE and HPLC. Finally CE, as merging techniques with very promising and interesting application of microscale analysis of drugs' binding parameters to immobilized bio-polymers is examined.

Development and characterization of an immobilized enzyme reactor based on glyceraldehyde-3-phosphate dehydrogenase for on-line enzymatic studies

The glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has been extensively studied as a target for new drugs to be used in the treatment of various parasitic diseases. The standard approach to the determination of GAPDH activity utilizes solubilized free enzyme and is limited by the enzyme's low stability. In the current study the stability of GAPDH was significantly increased through the covalent immobilization of the enzyme on a wide-pore silica support containing glutaraldehyde (Glut-P). The optimal conditions for the immobilization were: 100 mg Glut-P stationary phase, approximately 150 microg of enzyme dissolved in pyrophosphate buffer (15 mM, pH 8.5). The mixture was gently agitated for 6 h at 4 degrees C. Under these conditions 91.3% of protein was immobilized on 100 mg of Glut-P support with retention of 2.97% of the initial enzymatic activity. The activity of the immobilized GAPDH was stable for over 30 days. The GAPDH-Glut-P stationary phase was packed into a glass column to produce a GAPDH immobilized enzyme reactor (GAPDH-IMER). The activity and kinetic parameters of the GAPDH-IMER were investigated and the results demonstrated that the enzyme retained its activity and sensitivity to the competitive inhibitor agaric acid.

Immobilized nicotinic receptor stationary phases: going with the flow in high-throughput screening and pharmacological studies

The nicotinic acetylcholine receptor (nAChR) subtypes alpha3beta4-nAChR and alpha4beta2-nAChR have been immobilized and the resulting stationary phases used to determine binding affinities. The alpha3beta4-nAChR column was coupled to a C(18) column and a mixture of 18 compounds was sorted into ligands and non-ligands for the alpha3beta4-nAChR. The results demonstrate that the nAChR stationary phases can be used for on-line high-throughput screening (HTS).

Assessment of intraparticle biocatalytic distributions as a tool in rational formulation

Research has shown that the intraparticle biocatalytic distribution has extensive effects on the properties of various (industrial) biocatalytic particles and their performance in (bio-) chemical reactions. In recent years, advances in molecular chemistry have led to the development of many different specific (immuno-) labeling and light-microscopic detection techniques. Furthermore, high-quality image-digitizing devices and enhanced computing power have made image analysis readily accessible. These technologies may lead to the assessment and improvement of the internal biocatalyst profile as an integral part of biocatalytic particle optimization.