Use of compact, porous units with immobilized ligands with high molecular masses in affinity chromatography and enzymatic conversion of substrates with high and low molecular masses

Bioaffinity chromatography on monolithic supports

Affinity chromatography on monolithic supports is a powerful analytical chemical platform because it allows for fast analyses, small sample volumes, strong enrichment of trace biomarkers and applications in microchips. In this review, the recent research using monolithic materials in the field of bioaffinity chromatography (including immunochromatography) is summarized and discussed. After giving an introduction into affinity chromatography, information on different biomolecules (antibodies, enzymes, lectins, aptamers) that can act as ligands in bioaffinity chromatography is presented. Subsequently, the history of monoliths, their advantages, preparation and formats (disks, capillaries and microchips) as well as ligand immobilization techniques are mentioned. Finally, analytical and preparative applications of bioaffinity chromatography on monoliths are presented. During the last four years 37 papers appeared. Protein A and G are still most often used as ligands for the enrichment of immunoglobulins. Antibodies and lectins remain popular for the analysis of mainly smaller molecules and saccharides, respectively. The highly porous cryogels modified with ligands are applied for the sorting of different cells or bacteria. New is the application of aptamers and phages as ligands on monoliths. Convective interaction media (epoxy CIM disks) are currently the most used format in monolithic bioaffinity chromatography.

Isolation of cell-free DNA from plasma by chromatography on short monolithic columns and quantification of non-apoptotic fragments by real-time polymerase chain reaction

Human plasma is an important medical substance and a raw material for production of various therapeutics. During blood sampling, storage and processing, genomic DNA is released into plasma from nucleated blood cells that are damaged in the course of the procedure. In order to determine the concentration of contaminating DNA in plasma, we developed a method for DNA isolation by using anion-exchange chromatography on a BIA Separations CIM (convective interaction media) diethylaminoethyl column. DNA was quantified by SYBR Green based real-time polymerase chain reaction. The concentration of cell-free, non-apoptotic DNA in plasma ranged between 0.06 and 22.5 ng/ml. As substantial volumes of plasma or whole blood are administered directly into the vascular system, a recipient is exposed to high amounts of cell-free DNA, several orders of magnitude higher than the amount found in other biologicals.

New monolithic enzymatic micro-reactor for the fast production and purification of oligogalacturonides

Fast production and purification of alpha-(1,4)-oligogalacturonides was investigated using a new enzymatic reactor composed of a monolithic matrix. Pectin lyase from Aspergillus japonicus (Sigma) was immobilized on CIM-disk epoxy monolith. Studies were performed on free pectin lyase and immobilized pectin lyase to compare the optimum temperature, optimum pH, and thermal stability. It was determined that optimum temperature for free pectin lyase and immobilized pectin lyase on monolithic support is 30 degrees C, and optimum pH is 5. Monolithic CIM-disk chromatography is one of the fastest liquid chromatographic method used for separation and purification of biomolecules due to high mass transfer rate. In this context, online one step production and purification of oligogalacturonides was investigated associating CIM-disk pectin lyase and CIM-disk DEAE. This efficient enzymatic bioreactor production of uronic oligosaccharides from polygalacturonic acid (PGA) constitutes an original fast process to generate bioactive oligouronides.

Monolithic bioreactors for macromolecules

Enzymes immobilized on solid-phase matrices have found various applications in biotechnology, molecular biology and molecular diagnostics and can serve as industrial catalysts and as specific reagents for analytical procedures. A wide range of supports have been utilized for immobilization among which particle-based supports are the most commonly implemented. Type of support used for immobilization is one of the key considerations in practical application due to different immobilization efficiency, ligand utilization and the mass transfer regime. The mass transfer between the mobile and the particulate stationary phase is often a bottleneck for the entire process due to slow pore diffusion of large molecules. In contrast, monoliths due to their structure enable almost flow-independent properties. Consequently, the overall behavior of the immobilized ligand reflects its intrinsic reaction kinetics. Therefore, such an immobilized system is expected to allow higher throughput because of higher enzyme efficiency, especially pronounced for macromolecular substrates having low mobility. In this work, different methods for immobilization of enzymes on Convective Interaction Media monolithic supports are presented. In particular, enzymes acting on macromolecular substrates, such as trypsin, deoxyribonuclease and ribonuclease, are described in detail. Immobilized efficiency is evaluated for different immobilization procedures in terms of biologic activity and long-term stability. Finally, their performance on real samples is demonstrated.

Mammalian plasma membrane proteomics

Plasma membrane proteins serve essential functions for cells, interacting with both cellular and extracellular components, structures and signaling molecules. Additionally, plasma membrane proteins comprise more than two-thirds of the known protein targets for existing drugs. Consequently, defining membrane proteomes is crucial to understanding the role of plasma membranes in fundamental biological processes and for finding new targets for action in drug development. MS-based identification methods combined with chromatographic and traditional cell-biology techniques are powerful tools for proteomic mapping of proteins from organelles. However, the separation and identification of plasma membrane proteins remains a challenge for proteomic technology because of their hydrophobicity and microheterogeneity. Creative approaches to solve these problems and potential pitfalls will be discussed. Finally, a representative overview of the impressive achievements in this field will also be given.

Influence of the methacrylate monolith structure on genomic DNA mechanical degradation, enzymes activity and clogging

The chromatography of mechanically sensitive macromolecules still represents a challenge. While larger pores can reduce the mechanically induced cleavage of large macromolecules and column clogging, the column performance inevitably decreases. To investigate the effect of pore size on the mechanical degradation of DNA, column permeability and enzyme biological activity, methacrylate monoliths with different pore sizes were tested. Monolith with a 143 nm pore radius mechanically damaged the DNA and was clogged at flow rates above 0.5 ml min(-1) (26 cm h(-1)). For monoliths with a pore radius of 634 nm and 2900 nm, no mechanical degradation of DNA was observed up to 5 ml min(-1) (265 cm h(-1)) above which the HPLC itself became the main source of damage. A decrease of a permeability appeared at flow rate 1.8 ml min(-1) (95 cm h(-1)) and 2.3 ml min(-1) (122 cm h(-1)), respectively. The effect of the pore size on enzyme biological activity was tested with immobilized DNase and trypsin on all three monoliths. Although the highest amount of enzyme was immobilized on the monolith with the smallest pores, monolith with the pore radius 634 nm exhibited the highest DNase biological activity probably due to restricted access for DNA molecules into the small pores. Interestingly, specific biological activity was increasing with a pore size decrease. This was attributed to higher number of contacts between a substrate and immobilized ligand.

Use of monolithic supports in proteomics technology

An overview on the utilization of monoliths in proteomics technology will be given. Both silica- and polymer-based monoliths have broad use for microseparation of tryptic peptides in reversed-phase (RP) mode before identification by mass spectrometry (MS) or by MS/MS. For two-dimensional (2D) LC separation of peptides before MS or MS/MS analysis, a combination of ion-exchange, usually cation-exchange (CEX) chromatography with RP chromatography on monolithic supports can be employed. Immobilized metal ion affinity chromatography monoliths with immobilized Fe3+-ions are used for the isolation of phosphopeptides. Monoliths with immobilized affinity ligands are usually applied to the rapid separation of proteins and peptides. Miniaturized reactors with immobilized proteolytic enzymes are utilized for rapid on- or offline digestion of isolated proteins or protein mixtures prior to identification by LC-MS/MS. Monoliths also have broad potential for application in sample preparation, prior to further proteomic analyses. Monolithic supports with large pore sizes can be exploited for the isolation of nanoparticles, such as cells, organelles, viruses and protein aggregates. The potential for further adoption of monolithic supports in protein separation and enrichment of low abundance proteins prior to proteolytic digestion and final LC-MS/MS protein identification will be discussed.

Affinity monolith chromatography

The combined use of monolithic supports with selective affinity ligands as stationary phases has recently given rise to a new method known as affinity monolith chromatography (AMC). This review will discuss the basic principles behind AMC and examine the types of supports and ligands that have been employed in this method. Approaches for placing affinity ligands in monoliths will be considered, including methods based on covalent immobilization, biospecific adsorption, entrapment, and the formation of coordination complexes. Several reported applications will then be presented, such as the use of AMC for bioaffinity chromatography, immunoaffinity chromatography, immobilized metal-ion affinity chromatography, dye-ligand affinity chromatography, and biomimetic chromatography. Other applications that will be discussed are chiral separations and studies of biological interactions based on AMC.

Use of short monolithic columns for isolation of low abundance membrane proteins

Convective interaction media (CIM) monoliths provide a stationary phase with a high binding capacity for large molecules and are capable of high flow rates at a very low pressure drop. Used as anion- and cation-exchangers or with affinity ligands such as antibodies, these columns have the potential for processing large volumes of complex biological mixtures within a short time. In the present report, monoclonal antibodies against several rat liver plasma membrane proteins were bound and cross-linked to protein A or protein G CIM affinity columns with a bed volume of only 60 microL. Antigens recognized by bound antibodies and co-eluting (interacting) proteins were rapidly isolated in a single step from either total plasma membrane extracts or subfractions isolated using anion-exchange CIM disk-shaped columns. The isolated antigens and co-eluting proteins were subsequently identified by immunoblot or by LC-MS/MS.

Immobilization of deoxyribonuclease via epoxy groups of methacrylate monoliths. Use of deoxyribonuclease bioreactor in reverse transcription-polymerase chain reaction

A deoxyribonuclease bioreactor was prepared by immobilization of deoxyribonuclease I through epoxy groups inherently present on poly (glycidyl methacrylate-co-ethylene dimethacrylate) monoliths. Columns with various levels of DNase activity were prepared varying immobilization temperature, pH, time and method. The apparent Michaelis-Menten constant, Km(app), and turnover number, k3app, for immobilized DNase determined by on-line frontal analysis method were, respectively, 0.28 g of DNA l(-1) and 16 dA260nm min(-1) mg(-1) of immobilized DNase. The highest activity of immobilized DNase was detected at 1 mM calcium ions concentration and mirrored properties of free enzyme; however, reaction temperature in the range from 25 to 37 degrees C has no significant effect on activity of immobilized DNase in contrary to free enzyme. The CIM DNase bioreactor was used for elimination of DNA contaminants in RNA samples prior to reverse transcription followed by PCR.

Short monolithic beds: history and introduction to the field

The history of the development of short monolithic beds is described.

Affinity purification and enzymatic cleavage of inter-alpha inhibitor proteins using antibody and elastase immobilized on CIM monolithic disks

Epoxy-activated monolithic CIM disks seem to be excellent supports for immobilization of protein ligands. The potential use of enzymes, immobilized on monolithic disks for rapid preparative cleavage proteins in solution was investigated. Digestion of complex plasma proteins was demonstrated by using inter-alpha inhibitors with elastase, immobilized on epoxy-activated CIM disks. Recently, a monoclonal antibody against human inter-alpha inhibitor proteins (MAb 69.31) was developed. MAb 69.31 blocks the inhibitory activity of inter-alpha inhibitor proteins to serine proteases. These results suggest that the epitope defined by this antibody is located within or proximal to the active site of the inhibitor molecule. This antibody, immobilized on monolithic disk, was used for very rapid isolation of inter-alpha proteins. The isolated complex protein was used for enzymatic digestion and isolation of cleavage products, especially from inter-alpha inhibitor light chain to elucidate precisely the target sequence for MAb 69.31 by N-terminal amino acid sequencing. Bovine pancreatic elastase immobilized on monolithic disk cleaves inter-alpha inhibitor protein complex into small fragments which are still reactive with MAb 69.31. One of these proteolytic fragments was isolated and partially sequenced. It could be shown that this sequence is located at the beginning of two proteinase inhibitor domains of the inter-alpha inhibitor light chain (bikunin). Elastase immobilized on monolithic disk offers a simple and rapid method for preparative isolation of protease cleavage fragments. The immobilized enzyme is stable and still active after repeated runs. A partial or complete digestion can be achieved by varying the flow rate.

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.

Affinity processes realized on high-flow-through methacrylate-based macroporous monoliths

The technology for preparation of rigid macroporous polymers suggested in the late 1980s has become a powerful instrument for the development of a novel scientific and practical field. At present, monolithic stationary phases are widely used in the processes of bioseparation (chromatography), bioconversion (enzyme reactors) as well as in other processes based on interphase mass distribution (for example, solid phase peptide and oligonucleotide synthesis). Bioaffinity modes of suggested dynamic methods are very promising for their use in different analytical processes (immunological, ecological, medical and other types of analytical monitoring), preparative isolation of blood proteins such as myoglobin, hemoglobin, immunoglobulins, etc. and also recombinant products directly from cell supernatants or lysates. For the first time, it has been shown that bioaffinity pairing with participation of immobilized on carefully designed rigid supports is very fast and the whole process of affinity separation can be realized within second time scale. The principle of bioaffinity recognition is generaly at the construction of biological reactors (for example, enzyme reactors). Improved kinetics of biocatalized reactions is explained by a minimal influence on the surface of the used sorbent. Very perspective field is the use of discussed monoliths for solid phase chemical synthesis of fragments of biological macromolecules (peptides and oligonucleotides). Several examples of these applications will be presented and discussed.

Biospecific immobilization of mannan-penicillin G acylase neoglycoenzyme on Concanavalin A-bead cellulose

The matter of this work was to evaluate possibilities of biospecific immobilization of synthetic mannan-penicillin G acylase neoglycoconjugate on Concanavalin A support. The conjugate containing 37% (w/w) of yeast mannan was prepared. Significant biospecific interaction of this neoglycoenzyme with Con A was confirmed by precipitation method. The biospecific sorption of conjugate was investigated using Concanavalin A-triazine bead celluloses MT-100 with different content of Con A (from 1.4 to 9.8 mgCon A/gwet support). The results obtained under optimal conditions were compared with those from covalent immobilization of PGA. The sorbent capacity was observed higher for covalent binding of enzyme. On the other hand, the biospecifically immobilized neoglycoenzyme retained a greater amount of initial activity. The maximum amount of 6.6mgimmobilizedneoglycoenzyme/gwet Con A-sorbent (18.1 U/g) was achieved. The amount as well as activity of immobilized mannan-penicillin G acylase was increased by its two multiple layering on surface of sorbent (10.1mg, respectively, 23.5 U/gwet sorbent). Determined storage and operational (using flow calorimetric method) stabilities of biospecifically immobilized enzyme, were similar, possibly somewhat higher that those of covalent bound penicillin G acylase.

Convective Interaction Media (CIM)--short layer monolithic chromatographic stationary phases

Modern downstream processing requires fast and highly effective methods to obtain large quantities of highly pure substances. Commonly applied method for this purpose is chromatography. However, its main drawback is its throughput since purification, especially of large molecules, requires long process time. To overcome this problem several new stationary phases were introduced, among which short layer monoliths show superior properties for many applications. The purpose of this review is to give an overview about short methacrylate monolithic columns commercialised under the trademark Convective Interaction Media (CIM). Their unique properties are described from different perspectives, explaining reasons for their application on various areas. Approaches to prepare large volume methacrylate monolithic column are discussed and optimal solutions are given. Different examples of CIM monolithic column implementation are summarised in the last part of the article to give the reader an idea about their advantages.

Enzyme immobilization on epoxy- and 1,1′-carbonyldiimidazole-activated methacrylate-based monoliths

Monolithic Convective Interaction Media (CIM) have been activated with epoxide and imidazole carbamate functionalities and used as supports for covalent immobilization of protein A, deoxyribonuclease I, and trypsin. The efficiency of immobilization for these proteins was determined from the amount of bound IgG, degradation of DNA, and hydrolysis of Nalpha-benzoyl-L-arginine ethyl ester, respectively. The respective biological activities of trypsin and the binding capacity of protein A immobilized via imidazole carbamate groups were 11.45 and 2.25 times higher than those obtained for epoxide matrix while they were practically equal for deoxyribonuclease I. The kinetics of immobilization was studied in detail for trypsin under dynamic conditions and revealed that the enzyme immobilized via imidazole carbamate groups already reached its highest activity in 5 min. In contrast, a much longer time was required for immobilization via epoxy groups.

Preparative and analytical chromatography of pegylated myelopoietin using monolithic media

Monolithic media were compared with Q- and SP-Sepharose high performance chromatography for preparative purification and with Q- and SP-5PW chromatography for analysis of a pegylated form of myelopoietin (MPO), an engineered hematopoietic growth factor. The use of either monolithic or Sepharose based supports for preparative chromatography produced highly purified pegylated MPO with the monolithic media demonstrating peak resolution and repeatability at flow rates of 1 and 5 ml/min resulting in run times as much as five-fold shorter compared to Sepharose separations. The monolithic disks also resulted in 10-fold shorter run times for the analytical chromatography, however, their chromatographic profiles and peak symmetry were not as sharp compared to their Q-5PW and SP-5PW counterparts.

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.

Characterization of CIM monoliths as enzyme reactors

The immobilization of the enzymes citrate lyase, malate dehydrogenase, isocitrate dehydrogenase and lactate dehydrogenase to CIM monolithic supports was performed. The long-term stability, reproducibility, and linear response range of the immobilized enzyme reactors were investigated along with the determination of the kinetic behavior of the enzymes immobilized on the CIM monoliths. The Michaelis-Menten constant K(m) and the turnover number k(3) of the immobilized enzymes were found to be flow-unaffected. Furthermore, the K(m) values of the soluble and immobilized enzyme were found to be comparable. Both facts indicate the absence of a diffusional limitation in immobilized CIM enzyme reactors.

Very fast analysis of impurities in immunoglobulin concentrates using conjoint liquid chromatography on short monolithic disks

Transferrin and albumin are often present in immunoglobulin G (IgG) concentrates and are considered as impurities. Therefore, it is important to determine their concentration in order to obtain a well-characterized biological product. Here, we describe their determination based on conjoint liquid chromatography (CLC). The established method combines two different chromatographic modes in one step: affinity and ion-exchange chromatography (IEC) combined in one column. Therefore, two CIM Protein G and one CIM quaternary amine (QA) monolithic disks were placed in series in one housing forming a CLC monolithic column. Binding conditions were optimized in a way that immunoglobulins were captured on the CIM Protein G disks, while transferrin and albumin were bound on the CIM QA disks. Subsequently, transferrin and albumin were eluted separately by a stepwise gradient with sodium chloride, whereas immunoglobulins were released from the Protein G ligands by applying low pH. A complete separation of all three proteins was achieved in less than 5 min. The method permits the quantification of albumin and transferrin in IgG concentrates and has been successfully validated.

Miniaturized membrane-based reversed-phase chromatography and enzyme reactor for protein digestion, peptide separation, and protein identification using electrospray ionization mass spectrometry

A commonly used capillary fitting is employed for housing miniaturized membrane chromatography for performing reversed-phase peptide separations. By placing a hydrophobic and porous polyvinylidene fluoride membrane around the end of a polymer sleeve, the assembly of capillary fitting not only provides the stationary phase, but also establishes the necessary flow paths using capillary connections. The miniaturized membrane chromatography system is coupled with a micro-enzyme reactor containing immobilized trypsins for performing rapid protein digestion, peptide separation, and protein identification using electrospray ionization mass spectrometry. Separation performance of cytochrome c digest in miniaturized membrane chromatography is compared with the results obtained from micro-LC and capillary LC. The efficacy and the potentials of miniaturized membrane chromatography in tryptic mapping are reported. The use of miniaturized membrane chromatography allows significant reduction in sample consumption together with enhanced detection sensitivity. By minimizing the void volume in miniaturized membrane chromatography, the elution times of cytochrome c peptides are significantly shortened in this study in comparison with our previous results, and are comparable with those in micro-LC and capillary LC using considerably higher mobile phase flow-rates.

Chromatographic reactors based on biological activity

In the last decade there were many papers published on the study of enzyme catalyzed reactions performed in so-called chromatographic reactors. The attractive feature of such systems is that during the course of the reaction the compounds are already separated, which can drive the reaction beyond the thermodynamic equilibrium as well as remove putative inhibitors. In this chapter, an overview of such chromatographic bioreactor systems is given. Besides, some immobilization techniques to improve enzyme activity are discussed together with modern chromatographic supports with improved hydrodynamic characteristics to be used in this context.

Short monolithic columns as stationary phases for biochromatography

Monolithic supports represent a novel type of stationary phases for liquid and gas chromatography, for capillary electrochromatography, and as supports for bioconversion and solid phase synthesis. As opposed to individual particles packed into chromatographic columns, monolithic supports are cast as continuous homogeneous phases. They represent an approach that provides high rates of mass transfer at lower pressure drops as well as high efficiencies even at elevated flow rates. Therefore, much faster separations are possible and the productivity of chromatographic processes can be increased by at least one order of magnitude as compared to traditional chromatographic columns packed with porous particles. Besides the speed, the nature of the pores allows easy access even in the case of large molecules, which make monolithic supports a method of choice for the separation of nanoparticles like pDNA and viruses. Finally, for the optimal purification of larger biomolecules, the chromatographic column needs to be short. This enhances the speed of the separation process and reduces backpressure, unspecific binding, product degradation and minor changes in the structure of the biomolecule, without sacrificing resolution. Short Monolithic Columns (SMC) were engineered to combine both features and have the potential of becoming the method of choice for the purification of larger biomolecules and nanopartides on the semi-preparative scale.

Application of monoliths as supports for affinity chromatography and fast enzymatic conversion

Monoliths are useful chromatographic supports, as their structure allows improved mass transport. This results in fast separation. Once the ligand of interest has been immobilized, chromatographic separation can also be accomplished in affinity mode. Ligands with low molecular mass have been shown to be the easiest to immobilize. Nowadays, ligands with low molecular mass are often designed by combinatorial chemical techniques. In addition, many applications have been described where ligands with high molecular mass, such as Proteins A and G, antibodies, lectins and receptors are used. The immobilization of an enzyme on the monolithic support creates a flow-through reactor. Small proteins, such as carbonic anhydrase, can be directly immobilized on the support. However, in the case of large molecules, the active center of the enzyme is no longer accessible at all or only to a limited degree. An improvement can be achieved by introducing a spacer, which allows maximum enzymatic conversion. Fast conversion of substrates with high molecular mass has been investigated with immobilized trypsin. It was shown that in case of high-molecular-mass substrates, the conversion rate depends very much on the flow-rate. Most applications described have been performed on an analytical or semi-preparative scale. However, the technical problems of up-scaling are close to being definitely solved, enabling enzymatic conversion on a preparative scale in the future.

On-line coupling of micro-enzyme reactor with micro-membrane chromatography for protein digestion, peptide separation, and protein identification using electrospray ionization mass spectrometry

To miniaturize high-performance membrane chromatography, a poly(vinylidene fluoride) membrane medium, employed as the stationary phase, is sandwiched between two poly(dimethylsiloxane) substrates containing the microchannels. The microchannels are fabricated by the capillary molding technique, involving the use of capillaries as the channel template and the fluid inlet/outlet. The micro(micro)-membrane chromatography system is coupled with a micro-enzyme reactor containing immobilized trypsins for performing rapid protein digestion, peptide separation, and protein identification using electrospray ionization mass spectrometry. Separation performance of cytochrome c digest in micro-membrane chromatography is compared with the results obtained from a regular reversed-phase micro-liquid chromatography. The efficacy and the potentials of micro-membrane chromatography in tryptic mapping are reported. On-line integration of the micro-enzyme reactor with micro-chromatographic separation techniques and electrospray ionization mass spectrometry clearly provides a microanalytical platform for automated sample handling, minimized sample loss, and reduced sample consumption. It also provides enhanced detection sensitivity and dynamic range for the analysis of complex protein mixtures such as cell lysates in proteomics research.

Monoliths as stationary phases for separation of proteins and polynucleotides and enzymatic conversion

Monoliths are considered as a novel generation of stationary phases. They were applied for capillary electrochromatography and liquid chromatography exploiting every action principle such as ion-exchange, affinity recognition, reversed-phase, and hydrophobic interaction. The fast separation was explained by convective transport of the solutes through the bed. The contribution of this mode of transport is similarly explained as done for the beds packed with particles with gigapores. For monolithic beds, the concept of an ultrashort bed was frequently used. This mode of operation allows very short separation time. In many cases a gradient elution is necessary to achieve separation. Examples of applications for protein and polynucleotide separation performed on monoliths are given. Enzymatic conversion was described showing the examples of several immobilzed enzymes.

On-line characterization of the activity and reaction kinetics of immobilized enzyme by high-performance frontal analysis

A microreactor by immobilized trypsin on the activated glycidyl methacrylate-modified cellulose membrane packed column was constructed. Immobilized trypsin mirrored the properties of the free enzyme and showed high stability. A novel method to characterize the activity and reaction kinetics of the immobilized enzyme has been developed based on the frontal analysis of enzymatic reaction products, which was performed by the on-line monitoring of the absorption at 410 nm of p-nitroaniline from the hydrolysis of N-alpha-benzoyl-DL-arginine-p-nitroanilide (BAPNA). The hydrolytic activity of the immobilized enzyme was 55.6% of free trypsin. The apparent Michaelis-Menten kinetics constant (Km) and Vmax values measured by the frontal analysis method were, respectively, 0.12 mM and 0.079 mM min(-1) mg enzyme(-1). The former is very close to that observed by the static and off-line detection methods, but the latter is about 15% higher than that of the static method. Inhibition of the immobilized trypsin by addition of benzamidine into substrate solution has been studied by the frontal analysis method. The apparent Michaelis-Menten constant of BAPNA (Km), the inhibition constant of benzamidine (Ki) and Vmax were determined. It was indicated that the interaction of BAPNA and benzamidine with trypsin is competitive, the Km value was affected but the Vmax was unaffected by the benzamidine concentration.