Eliminating disulfide exchange during glutamyl endopeptidase digestion of native protein

Numerous advantages of using immobilized enzymes over free-solution protein digests have been cited in the literature. This investigation examines both the rate of hydrolysis and the extent of disulfide bond exchange in disulfide bridged dipeptide fragments formed during proteolysis of native protein. Glutamyl endopeptidase as both an immobilized enzyme and in free solution was used in these studies. It was found that extensive hydrolysis of insulin was achieved in 2 min with immobilized enzyme cartridges operated in the stopped-flow mode orders. This is orders of magnitude faster than was seen in free solution. Other advantages ranging from ease of use and reduction in sample size to the potential for automation were also noted with the immobilized enzyme cartridge. Normal free-solution proteolysis generally requires 12-24 h, based on the lower enzyme-to-substrate ratio in solution. A disturbing feature noted in these lengthy free-solution reactions was the tendency to form disulfide bridged peptide artifacts. This could lead to the erroneous conclusion that disulfide bonding in a sample was not that of the native protein. It is concluded that the advantage of immobilized enzymes over free-solution reactions will be most important in the pharmaceutical industry where proteolytic fragment "fingerprinting" of recombinant proteins is being used to confirm structure.

Electrokinetically-driven cation-exchange chromatography of proteins and its comparison with pressure-driven high-performance liquid chromatography

This paper examines protein ion-exchange behavior in electrokinetically-driven open-tubular chromatography with columns produced by immobilization of poly(aspartic acid) on capillary walls. Retention and selectivity are similar in the electrokinetic elution mode to that observed in HPLC. The separation mechanism was found to depend on the relationship of mobile phase pH to that of protein pI and ionic strength. Column efficiency in the electrokinetic elution mode was found to be 10-100-times higher than in HPLC. The best separations were achieved at intermediate ionic strength and high pH. The great advantage of these low-phase-ratio, high-efficiency open tubular columns is that isocratic separations in the electrokinetic elution mode were equivalent to gradient elution in the HPLC mode. Low phase ratio has the net effect of collapsing the chromatogram into a narrow elution window while the very high efficiency produces the requisite resolution.

Capillary electrochromatography of peptides in a microfabricated system

Reversed-phase liquid chromatography of tryptic peptides is shown in the capillary electrochromatography mode using microfabricated columns. Although selectivity is different, a mixture of tryptic peptides from ovalbumin appears to be as easily separated in the CEC as HPLC mode. The major difference between a separation in the macrofabricated CEC column and conventional separations in the HPLC mode is that separations are more readily achieved in the isocratic mode in the lower surface area microfabricated CEC columns.

The in vitro displacement of adsorbed model antigens from aluminium-containing adjuvants by interstitial proteins

Vaccines prepared by adsorbing an antigen onto an aluminium-containing adjuvant are usually administered by intramuscular or subcutaneous injection. The vaccine then comes in contact with interstitial fluid which contains proteins. In vitro displacement studies were performed to determine whether antigens, which are adsorbed to aluminium-containing adjuvants, can be displaced by interstitial proteins. It was found that when previously adsorbed model antigens such as lysozyme or myoglobin were exposed to interstitial proteins such as albumin or fibrinogen that extensive displacement occurred. A factorial study of the displacement of myoglobin from aluminium hydroxide adjuvant by albumin was performed. The displacement occurred rapidly with the majority of the displacement occurring in less than 15 min. Whether the concentration of the adsorbed myoglobin was above or below the adsorptive capacity of the aluminium hydroxide adjuvant affected the amount which could be displaced. Less myoglobin was displaced when the concentration was below the adsorptive capacity. The age of the model vaccine (1, 2 or 7 days) prior to exposure to the interstitial protein did not influence the amount of myoglobin that was displaced. The affinity of model antigens and interstitial proteins for aluminium hydroxide or aluminium phosphate adjuvant was characterized by the adsorption coefficient in the Langmuir equation. In every case studied, the protein having the larger adsorption coefficient was able to displace the protein with the smaller adsorption coefficient.

Chromatography and electrophoresis on chips: critical elements of future integrated, microfluidic analytical systems for life science

Liquid chromatography and electrophoresis played a major role in the life-science revolution, most strikingly in protein purification, peptide fractionation and sequencing, amino acid analysis, and DNA sequencing. The objective of this article is to examine the potential role of separation systems in the continuing evolution of biochemistry, biotechnology and molecular biology. Very small chip-based systems may change how chemical analyses in biology, medical research and health care evolve over the next decade.

Metallocenes as cationizing agents in the characterization of polystyrenes and polyethylene glycols by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Very little work has been done on exploring the transition metals as suitable cationizing agents for the analysis of polymers by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF). This paper reports on the characterization of polystyrenes and polyethylene glycols with select metallocenes as cationizing agents. It was found that ferrocene, nickelocene and cobaltocene did indeed cationize the polymer and that, at higher molecular weights, very little if any metal clusters were observed. It was also found that the signal intensity was improved for the higher molecular weight polymers.

Protein-protein interactions on weak-cation-exchange sorbent surfaces during chromatographic separations

This paper examines the nature of chromatographic separations on a weak cation-exchange material in which immobilized protein coats 24% or less of the sorbent surface. It was found that columns on which proteins were immobilized still behaved as a cation-exchange chromatography sorbents, but their selectivity was different from the parent weak cation-exchange column. This was interpreted to mean that in addition to the normal electrostatic interactions expected in ion- exchange chromatography, protein analytes interact with immobilized protein on the sorbent surface. Anionic proteins were not adsorbed, indicating that immobilized proteins were acting synergistically with ionic stationary phase groups to enhance retention. It is concluded that these protein-protein interactions occur after proteins are captured by the primary interaction mechanism of the column, in this case, electrostatic interaction. Protein-protein interaction is a secondary, lateral process. These lateral interactions were observed between 4% and 24% surface saturation. The significance of this observation is that in preparative chromatography and the case of "fouled" columns, strongly adsorbed proteins could alter the elution characteristics of sample proteins being target for analysis or purification.

Rapid verification of disulfide linkages in recombinant human growth hormone by tandem column tryptic mapping

An automated tryptic mapping method was developed for characterization of disulfide linkages in recombinant human growth hormone (rhGH). The hormone was trypsin digested and the peptide fragments concentrated by eluting rhGH through an immobilized trypsin column and transferring the peptides directly to a reversed-phase liquid chromatography (RP-LC) column where they were collected. Reaction time was controlled by the flow-rate. Following tryptic digestion of a sample, the immobilized enzyme column was uncoupled from the flow train by a switching valve and the RP-LC column eluted with a solvent gradient ranging from 0.1% trifluoroacetic acid (TFA) with 1% acetonitrile (ACN) to ACN with 0.1% TFA and 5% water. This two-step mapping process was achieved within 2 h on both native and reduced rhGH samples. The chromatographic elution position and mass spectra matrix-assisted laser desorption ionization time-of-flight mass spectrometry of native rhGH and sulfur-containing peptides were determined with standards. Standards of the individual sulfhydryl (-SH) containing peptides and all possible disulfide linked peptides that could result from coupling the -SH peptides in disulfide linkages were obtained by synthesis and chromatographic purification. This approach allowed the chromatographic elution position of all possible mismatched disulfide containing peptides to be established and samples of rhGH to be examined for improper folding.

Lateral interaction between electrostatically adsorbed and covalently immobilized proteins on the surface of cation-exchange sorbents

This paper examines the nature of chromatographic separations on a weak cation-exchange material in which immobilized proteins coats 50% or less of the sorbent surface. It was found that although these sorbents still function as cation exchangers, covalently immobilized proteins frequently contribute to the ion-exchange behavior of some protein analytes. Chromatographic retention of analytes was equal to or greater on immobilized protein derivatized columns than underivatized sorbents. Anionic proteins, in contrast, were not adsorbed, indicating that immobilized proteins were acting synergistically with ionic stationary phase groups to enhance retention. It was concluded that electrostatic adsorption is a prerequisite for analyte protein/immobilized protein interactions of sufficient magnitude to impact ion-exchange separations. Large differences in protein resolution were observed on columns that were identical in all respects except for the immobilized protein, further confirming that analyte/immobilized protein interactions were unique to the interacting pair. The extent of interaction was also influenced by concentration of the immobilized protein in the case of lysozyme. Interactions between the analyte and immobilized protein were found to occur between both the same two proteins and dissimilar species. It was concluded that these phenomena are due to lateral interactions between immobilized proteins and analyte proteins subsequent to electrostatic adsorption of the analyte on the underivatized surface of ion-exchange sorbents.

Study of protein binding to a silica support with a polymeric cation-exchange coating

A silica-based, polyacrylate ion-exchange stationary phase has been prepared using Ce(IV) as the initiator. Analysis of the physical properties of the polymeric layer separated from the silica surface indicates that the polymeric coating is cross linked to some extent. The polymerization carried out at different concentrations of Ce(IV) demonstrated that the effective surface area can be increased by lowering the Ce(IV) concentration at higher monomer concentrations of the reaction mixture. These materials are quite reproducible and of high electrostatic binding capacity; 1.485 mumol/m2. The electrostatic binding capacity of a non-polymeric stationary phase reached the theoretical limit for a monolayer (0.16 mumol/m2). However, the covalent binding capacity of the same stationary phase was only 50% of the electrostatic binding capacity. The same trend was observed in all the polymeric stationary phases tested. This shows that the mechanism of protein binding in polymeric and conventional stationary phases is similar, and multilayer electrostatic binding is highly unlikely in these sorbents examined. Z numbers revealed that the contact area of the protein is independent of the polymeric character of the stationary phase and therefore, the increased loading of these polymeric stationary phases is due to the increased surface area.

Enzyme-linked immunosorbent assays in a chromatographic format

This paper describes the execution of enzyme-linked immunosorbent assays (ELISA), (i) in immunosorbent columns with antibodies immobilized on porous particles, (ii) where samples and reagents are metered by valves and syringe pumps, (iii) samples, reagents, substrate, and wash buffers are transported into or through the system by high pressure liquid chromatography pumps, and (iv) enzyme reaction product is detected by absorbance. The normal protocol used for ELISA was modified in that antigen was complexed with enzyme conjugated antibody in the autosampler and an aliquot introduced into the system where it was transported to the immunosorbent and captured. Substrate was subsequently pumped into the immunosorbent bed and the product swept to an absorbance detector for quantitation.

Chemiluminescent detection for capillary electrophoresis and EMMA enzyme assays

A large number of analytically and physiologically significant enzymes produce or consume hydrogen peroxide (H2O2). Post-column reaction of H2O2 with luminol in an alkaline solution results in chemiluminescence. A prototype reactor/detector for CE with chemiluminescent detection (CLD) of H2O2 was constructed and utilized. Two variations of the detection cell illustrated the difference between an analyte-limiting (stagnant-cell) and a window-limiting (swept-cell) detection scheme. The stagnant-cell detector had a low limit of detection (39 fmol at S/N = 3), but poor separation efficiency (1100 theoretical plates). The swept-cell detector demonstrated greater efficiency (226,000 theoretical plates), but a detection limit one order of magnitude higher (380 fmol). Several enzyme assays were developed using electrophoretically mediated microanalysis (EMMA) with chemiluminescent monitoring of H2O2. EMMA can be used to perform enzyme assays in a capillary format using electrophoretic mixing. Accumulated product of an incubation is swept to the detector and traditionally monitored by UV-VIS absorbance, fluorescence, or electrochemical detection. Higher sensitivity may also be obtained from the use of CLD. Chemical amplification with galactose oxidase and glucose oxidase resulted in the production of H2O2, while catalase enzymatically consumed H2O2. This work showed a CLD limit of 9300 molecules in the case of catalase.

Dynamic modeling of electrophoretically mediated microanalysis

A dynamic model is presented for simulation of reaction-based chemical analysis of enzymes and substrates in capillary electrophoretic systems by the methodology of electrophoretically mediated microanalysis (EMMA). The mathematical model utilizes mass balance expressions describing the time-dependent effects of electromigration, chemical reaction, and diffusional band broadening upon the concentration profiles of the various reagent and product species. The model is implemented in an iterative computer program in which the capillary is segmented into arrays of bins storing the concentration profiles of each of the chemical species. During each time increment, the effects of electrophoresis, reaction kinetics, and diffusion are calculated, and the concentrations stored in the arrays are updated. The flexibility of the model to accommodate various initial capillary conditions, sample introduction methods, and voltage programming allows diverse EMMA analyses to be simulated. The simulated results are shown to be in good qualitative agreement with experimental data for zonal injection and moving boundary EMMA determinations of leucine aminopeptidase as well as an EMMA analysis of ethanol.

Moving boundary electrophoretically mediated microanalysis

Moving boundary sample introduction is described as an alternative to zonal injection methods for the electrophoretically mediated microanalysis (EMMA) of leucine aminopeptidase (LAP). The capillary was initially filled with the analyte solution while the faster-migrating substrate, L-leucine-p-nitroanilide, was maintained in the inlet reservoir. Upon application of an electric field, electrophoretic merging of the reagents proceeded, and the detectable reaction product, p-nitroaniline, was transported to the detector. The area, maximum height, inclining slope, and declining slope of the resulting triangular product profile were each directly proportional to the activity of LAP, and the observed migration times of the product profile features defined the volume and time of the incubation. The moving boundary technique offered more than an order of magnitude greater concentration sensitivity than the zonal injection EMMA method. This heightened sensitivity facilitated rapid analysis as the use of elevated electric field strenghts and short capillaries allowed for a 24-s kinetic determination of LAP.

C-terminal ladder sequencing via matrix-assisted laser desorption mass spectrometry coupled with carboxypeptidase Y time-dependent and concentration-dependent digestions

The utility of matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry for the analysis of C-terminal peptide ladders from carboxypeptidase Y (CPY) digestions is discussed. MALDI analysis of aliquots of an optimized time-dependent CPY digestion of ACTH 7-38 fragment allowed for the sequence of the first 19 amino acids from the C-terminus to be determined in 25 min of digestion time. A strategy for performing parallel concentration-dependent digestions on the MAL-DI plate is proven to be superior to the time-dependent approach as the method development time and practical amounts of both peptide and enzyme consumed are reduced significantly. The on-plate approach offered the same sequence information from the ACTH 7-38 fragment and was used to digest 22 peptides of various amino acid composition, size, charge, and polarity. Of the 22 peptides digested on-plate, sequence information was derived from 19 of them. A statistical analysis strategy for ladder sequencing utilizing t-statistics is offered as a method for placing confidence intervals on residue assignments.

Capillary electrophoresis-based immunoassay for cortisol in serum

A competitive immunoassay for cortisol based on capillary electrophoresis (CE) and laser-induced fluorescence is described. The work involved the production of assay reagents and the development of separation conditions allowing for routine analysis of serum samples. Fluorescein-labeled cortisol was synthesized and purified. Fab fragments were produced from mouse monoclonal anticortisol antibody and purified using a POROS cation exchange chromatography column. After incubation of these reagents with serum, free and bound labeled antigen were separated by CE with high reproducibility. No prior sample cleanup of the serum samples was necessary. Serum calibration curves were established and used for the quantitation of cortisol in serum. The results demonstrate feasibility for a cortisol assay based on CE operating directly on serum samples.

Contribution of electrostatic and hydrophobic interactions to the adsorption of proteins by aluminium-containing adjuvants

The effect of ionic strength and ethylene glycol on the adsorption of bovine serum albumin (BSA) or lysozyme by a commercial aluminium hydroxide or aluminium phosphate adjuvant was studied at pH 7.4 and 25 degrees C. The adsorption of BSA by aluminium hydroxide adjuvant and lysozyme by aluminium phosphate adjuvant was found to be inversely related to ionic strength. This indicates that electrostatic attractive forces contribute to adsorption. The adsorption of lysozyme by aluminium phosphate adjuvant was reduced by the addition of ethylene glycol. However, no change in the adsorption of BSA by aluminium hydroxide adjuvant was noted when up to 40% ethylene glycol was present. This behaviour indicates that hydrophobic forces contribute to the adsorption of lysozyme but not of BSA. However, virtually no adsorption was observed when the protein and the adjuvant had the same surface charge. Thus, attractive forces may not be sufficient to produce adsorption of an antigen by an aluminium-containing adjuvant if electrostatic repulsive forces are present.

Selectivity in electrophoretically mediated microanalysis by control of product detection time

Differential electrophoretic mobility between an analyte and its product offers electrophoretically mediated microanalysis (EMMA) a unique capability to selectively control the detection time of the product of a reaction-based chemical analysis. If an analyte and its product differ in migration velocity under the influence of an applied electric field, the apparent velocity and, consequently, the detection time of the product are dependent upon the relative amounts of time the product effectively traverses the capillary with the respective mobilities of the analyte and the product. Consequently, by controlling when the analytical reaction is allowed to occur, the detection time of the reaction product can be selectively maneuvered within a time window defined by the mobilities of the analyte and the product. This paper describes the use of this technique to manipulate the detection time of product profiles independently of nonreacting matrix interferants for the determination of both enzymes and substrates by EMMA. Furthermore, the ability to manipulate product detection times allows for simultaneous EMMA determinations of multiple enzymes or substrates.

Rapid, automated, two-dimensional high-performance liquid chromatographic analysis of immunoglobulin G and its multimers

It is important to determine the amount of IgG multimers in immunoglobulin-containing pharmaceuticals because these aggregates can cause adverse reactions in patients. Previous methods for determining aggregates either suffered from interference of other proteins or required fraction collection and sample purification. A new, automated two-dimensional approach has been developed in which size-exclusion chromatography is performed in the first dimension followed by protein A affinity chromatography in the second dimension. This method is robust in that the aggregates are not disturbed by a preliminary purification step. Further, the presence of contaminating proteins has no effect on the analysis since affinity chromatography is used to determine the presence of IgG in the second dimension. The entire automated two-dimensional analysis can be performed in ca. 1 h.

Electrophoretically mediated micro-assay of alkaline phosphatase using electrochemical and spectrophotometric detection in capillary electrophoresis

Electrophoretically mediated micro-assays of alkaline phosphatase (ALP) are demonstrated in capillary electrophoretic systems using both electrochemical (ED) and spectrophotometric (UV) detection. In the ED mode, p-aminophenylphosphate was used as the substrate and p-aminophenol (pAP) was monitored at a carbon fiber electrode held at +180 mV vs. Ag/AgCl. Spectrophotometric detection was achieved using the substrate p-nitrophenylphosphate, and monitoring the product p-nitrophenol (pNP) at 405 nm. The detection limit for pAP by ED was determined to be 100-fold lower than for pNP using UV detection. In the determination of ALP, both methods were found to be linear. The detection limit for ALP using zero potential assays with UV detection was determined to be 1.8.10(-6) mg/ml compared to 1.8.10(-7) mg/ml using ED.

Electrophoretically mediated microanalysis of calcium

Electrophoretically mediated microanalysis (EMMA) was used for the determination of calcium. The faster analyte zone containing the calcium was injected spatially behind a slower zone of o-cresolphthalein complexone in a capillary electrophoresis based system. Upon application of the electric field the calcium zone was electrophoretically mixed with the reagent and product was formed. The bulk electroosmotic flow carried the product to the detector where the absorbance of the resulting complex at 575 nm was measured. Quantitation using an internal standard yielded a linear response with an R.S.D. of 8.1%. An inter-method comparison was performed with the standard bulk method and yielded results that did not significantly differ. The advantages of EMMA with respect to traditional methods were addressed.

Process monitoring of the production of gamma-interferon in recombinant Chinese hamster ovary cells

The production of recombinant gamma-interferon was monitored using high-performance liquid chromatographic methods. These methods were able to distinguish between glycosylated and non-glycosylated forms of gamma-interferon by complexing the carbohydrate with borate. Sufficient quantities of standard glycosylated gamma-interferon were not available for peak identification so immunological techniques were used to identify gamma-interferon variants. These techniques were validated with the non-glycosylated form. The non-glycosylated form was then shown to be retained only on a cation-exchange column, while the glycosylated form, complexed with borate, was retained only on an anion-exchange column. Samples were drawn at 2-h intervals over a 60-h production cycle and analyzed by both anion- and cation-exchange chromatography. Results indicated that the production of each form was coincidental and that the glycosylated form of gamma-interferon is produced in greater abundance than non-glycosylated.

Ensemble averaging and digital filtering in chromatography and electrophoresis

Ensemble averaging and digital filtering were implemented for signal-to-noise ratio improvement in the separation techniques of size-exclusion chromatography, immunoaffinity chromatography, capillary zone electrophoresis and capillary ion analysis. Results of ensemble averaging were always greater than statistically predicted. Techniques included five to nine replicate separations and yielded signal-to-noise improvement factors of 2.5 to 9.3. Running-average and time constant (RC)-convolution digital filters yielded increases in the signal-to-noise ratio ranging from zero to twelve. This paper will discuss and illustrate the usage of ensemble averaging and digital filtering in liquid-phase separation techniques.

Electrophoretically mediated microanalysis of ethanol

Capillary electrophoresis was used to determine ethanol by the methodology of electrophoretically mediated microanalysis (EMMA). In EMMA, spatially distinct analyte and analytical reagent zones of differing electrophoretic mobility are merged under the influence of an electric field, and the resulting product is transported to the detector. The enzymatic oxidation of ethanol to acetaldehyde by alcohol dehydrogenase was utilized, and the concurrent reduction of NAD+ to NADH was monitored at 340 nm as a measure of the quantity of ethanol injected. Quantitation using an internal standard and normalization for peak migration time yielded a R.S.D. of 2.7%, and the linear range extended to that quantity of ethanol which could be reacted prior to passing by the detection window. Comparison of the EMMA technique to the Sigma spectrophotometric procedure revealed that the two methods do not yield significantly different values for the determination of ethanol. The EMMA method offered the advantages of electrophoretic mixing and miniaturization.

Automated process monitoring of monoclonal antibody production

Antifibronectin, monoclonal antibody was monitored through 52 h of production. Samples were automatically drawn from a bioreactor into the injection valve of an HPLC system without prior sample preparation. The hybridoma cell line was nonadherent, so whole cells were injected directly onto the perfusable protein A affinity column. There was only a modest column back pressure (ca. 1700 psi at a linear flow rate of 1.5 cm/s) after over 75 injections over the 52-h experiment. These experiments demonstrate the utility of high-speed chromatography for rapid process monitoring.

Electrophoretically mediated microanalysis of leucine aminopeptidase in complex matrices using time-resolved laser-induced fluorescence detection

Leucine aminopeptidase, a clinically significant enzyme, was assayed in complex biological samples using a new technique termed electrophoretically mediated microanalysis. The assay was performed in capillary electrophoresis columns using time-resolved laser-induced fluorescence detection. Human serum, human urine, and Escherichia coli supernatant samples were assayed using this method. Results for serum and urine were within the ranges of expected values found in the literature. A low concentration of 6 x 10(-13) M enzyme in buffer was detected using this method. A detection limit (3 sigma) of 400 enzyme molecules in buffer was determined.

Mathematical treatment of electrophoretically mediated microanalysis

A new concept in reaction-based chemical analysis is introduced and theoretically described. By utilization of the variability in electrophoretic mobilities among charged species, spatially distinct zones of chemical reagents can be electrophoretically merged under the influence of an applied electric field. Electrophoretically mediated microanalysis (EMMA) exploits this phenomenon as a basis for chemical analysis utilizing capillary electrophoretic systems. EMMA is described in terms of the four stages required for reaction-based analysis: (1) analyte and analytical reagent metering; (2) initiation of reaction; (3) control of reaction conditions and product formation; (4) detection of species whose production or depletion is indicative of the concentration or quantity of the analyte of interest. The method is illustrated by the enzymatic oxidation of ethanol to acetaldehyde by alcohol dehydrogenase with the concurrent reduction of NAD+ to NADH monitored at 340 nm. Experimental results for both substrate and enzyme determinations are shown to agree with the presented theory.

Liquid chromatography based enzyme-amplified immunological assays in fused-silica capillaries at the zeptomole level

Through the use of fused-silica capillaries it was shown that reducing the liquid volume of an enzyme-amplified immunological assay increases the rate of amplification and sensitivity of the assay by several orders of magnitude. Human immunoglobulin G (hIgG) captured on protein G-coated 100-microns-i.d. columns was saturated with F(ab) anti-hIgG conjugated to alkaline phosphatase (ALP). Conjugated enzyme captured by the antigen was subsequently assayed in a stop-flow incubation with p-nitrophenyl phosphate. p-Nitrophenol produced in the stop-flow incubation was then swept to the detector and quantitated at 405 nm. The detection limit in the stop-flow mode was approximately 3 fmol. Three problems were identified in this flow-through, capillary assay format. The first was that the rate of immunological complex formation within the capillary was too slow. Preforming the immunological complex before application to the column increased the sensitivity by 2 orders of magnitude. Another problem was that the rate of mass transfer within the capillary limited capture of the preformed immunological complex. This problem was solved by stop-flow incubation of the complex in the column. The combination of preformation of the immunological complex and stop-flow binding within the column reduced the detection limit to approximately 3 amol. Finally, reducing the amount of F(ab)-ALP used in the assay minimized nonspecific binding of the conjugated enzyme and reduced the detection limit further to 333 zmol.

Native protein separations and enzyme microassays by capillary zone and gel electrophoresis

Native protein separations by capillary gel electrophoresis are achieved using linear acrylamide gel matrices. Polyacrylamide gels with a concentration range of 3.5-5% did not exhibit size separations for native proteins with molecular weights from 20,000 to 47,000. The separation of native proteins in gel-filled capillaries is based solely on the charge of the protein as in normal zonal electrophoresis. Retention of protein activity in the acrylamide matrix was demonstrated by performing enzymatic assays in the gel matrix. Alkaline phosphatase (ALP) and beta-galactosidase assays were conducted in both C18-PF108-modified and polyacrylamide gel-filled capillaries. Enzyme assays were achieved by filling the capillary with an appropriate substrate dissolved in the electrophoresis buffer. The product formed by the reaction of enzyme with substrate was monitored using a standard UV-visible detector. Both constant potential and zero potential modes of analysis were demonstrated. The polyacrylamide gel columns provide the advantages of minimized diffusion and limited band spreading due to the high viscosity of the gel matrix. The lowest detection limit achieved was 5.2 x 10(-20) mol (7.6 x 10(-12) M sample injected) of ALP. The dual enzyme assay of ALP and beta-galactosidase was achieved in gel-filled capillaries simultaneously.

Manipulation of electroosmotic flow in capillary electrophoresis

This paper reports the use of surfactant and polymer-C18 coated capillaries that allow manipulation of electroosmotic flow (EOF). Although this approach to the control of EOF involves the preparation and use of multiple capillaries, all the coatings were prepared by a single procedure. It is shown that the ability to control EOF allows optimization of both separation time and resolution. In the case of proteins, low EOF maximizes resolution whereas high flow gives the shortest analysis time. It should be noted that proteins are a special case and this conclusion may not be true with other molecular species. Through selection of a specific coating, it is possible to complete a separation in the shortest time while maintaining sufficient resolution to give baseline resolution of proteins. The various coated capillaries were examined in capillary zone electrophoresis (CZE) and capillary isoelectric focusing (cIEF) separations of native protein standards and hemoglobin variants. Separation of glycosylated hemoglobin A1 variants was achieved by cIEF within 10 min, including the focusing time. Good run-to-run reproducibility was obtained by flushing the capillary with the coating solution between analyses.

Rapid process monitoring in biotechnology

Detection of protein variants in the production of recombinant DNA products is an important and complex task. Rapid acquisition of this information permits feedback control of the production process and continuous validation of the product. Much of the technology required for rapid process monitoring is currently available or under development.

Immunochromatographic analysis of proteins. Identification, characterization and purity determination

Antibodies specific to a protein and its structural variants were immobilized on a high-performance Protein G column. This column recognized and selectively subtracted specific molecules from a sample. When a size-exclusion column was coupled with this high-performance affinity column, a comparison between the elution profile before and after the antibody immobilization was used to study antigen components present in the sample. Various human growth hormone structural variants and aggregates were studied using this approach. The technique is simple, fast and does not involve the usage of radioactive material.

Polymer- and surfactant-coated capillaries for isoelectric focusing

This paper reports a method for deactivation of fused-silica capillaries to be used in capillary isoelectric focusing (cIEF). Deactivation was achieved by adsorbing either a surfactant or hydrophilic polymer to alkylsilane-derivatized capillaries. The surfactant PF-108 and methyl cellulose reduced electro-osmotic flow (EOF) 20 to 30 fold in comparison to underivatized capillaries. Although EOF was reduced sufficiently to allow focusing to permit separations to be completed before proteins were swept through the capillary, there was adequate flow to obviate the need for a separate mobilization step. This reduces the complexity of cIEF and increases reproducibility. Based on resolution of hemoglobin variants, proteins that varied 0.03 pH units in isoelectric point were resolvable. This is equivalent to the highest resolution achieved in conventional slab and tube gel isoelectric focusing.

Fimbriated stationary phases for proteins

This paper describes synthetic procedures for preparing fimbriated stationary phases on poly(styrene-divinylbenzene) (PS-DVB) packing materials. The synthesis consists of a five-step procedure in which the order in which the steps are carried out may be varied. These steps are (i) polymerization of monomers to form an amphiphilic copolymer or oligomer, (ii) adsorption of either monomers, or polymer onto the PS-DVB surface, (iii) solvent induction of functional group orientation at the PS-DVB-polymer interface and polymer-water interface, (iv) a cross-linking reaction that forms a hydrophilic surface layer, and (v) derivatization of the surface layer with stationary phase.

Tandem chromatographic-immunological analyses

The function of conventional immuno-logical assays is to determine the presence and amount of known substances. Cross-reactivity of antibodies with unknown species of similar structure is a problem that can be circumvented by using chromatography in a second level of discrimination. Tandem LC-IA systems increase the selectivity and the sensitivity of assays by removing interfering species. For cases in which the goal is to prove that similar species are absent from a sample or to identify antigen variants, conventional assays fail. LC-IA systems are adept at dealing with these tasks. The necessary steps of metering reagents, separating Ag:Ab complex from other species, and enhancing detection in an immunological assay are easily accommodated by the LC system. In fact, the LC system provides a wide variety of new, high-sensitivity, high-speed methods for carrying out immunological assays. On the basis of the enormous versatility, selectivity, and sensitivity that LC-IA brings to analytical chemistry, we believe this technique will become increasingly important for monitoring analytes in complex biological matrices.

Contribution of soluble aluminium species to absorption of aluminium from the rat gut in situ

1. Rat gut perfusion studies in vivo at pH 4, 6 or 8 using aluminium chloride or equimolar aluminium chloride and sodium citrate showed that elevated plasma aluminium concentrations were associated with aluminium solubility in the perfusion. Elevated plasma aluminium levels and soluble aluminium in the perfusate occurred with perfusion of equimolar aluminium chloride and sodium citrate at all three pH values. 2. Partitioning studies in vitro, utilizing water and ethyl acetate, revealed that uncomplexed aluminium exhibited maximum partitioning into the ethyl acetate phase at pH 2.5. When complexed with citrate, aluminium exhibited partitioning over a much broader pH range, pH 2.5-8.0. 3. A direct linear relationship was observed between the soluble aluminium concentration of the perfusate and the increase in the plasma aluminium level, suggesting that soluble aluminium is absorbed by a passive diffusion mechanism.

Sodium dodecyl sulfate-capillary gel electrophoresis of proteins using non-cross-linked polyacrylamide

Proteins with relative molecular masses of 14,000 to 205,000 were separated by sodium dodecyl sulfate-capillary gel electrophoresis (SDS-CGE) using non-cross-linked linear polyacrylamide gels on both coated and uncoated fused-silica capillaries. It was determined that viscosity of the acrylamide solution was a major factor affecting column stability with linear acrylamide gels. When the viscosity of the acrylamide solution reaches 100 cP, electro-osmotically driven displacement of the gels is insignificant. Uncoated capillaries provided better resolution, stability, and reproducibility than surface coated capillaries when the concentration of linear polyacrylamide was greater than 4%. At lower gel concentrations, non-cross-linked polyacrylamide is easily displaced from the columns. A calibration plot of log molecular mass vs. mobility with non-linear polyacrylamide was linear, which indicated that resolution was equivalent to that obtained with cross-linked acrylamide. Separations with model proteins indicated that baseline resolution between protein species that vary 10% in molecular mass can be achieved.

Ultramicro enzyme assays in a capillary electrophoretic system

This paper describes an ultramicro method for achieving enzyme assays. Enzyme saturating concentrations of substrate, coenzyme when appropriate, and running buffer were mixed and used to fill a deactivated fused-silica capillary in a capillary zone electrophoresis apparatus. The enzyme glucose-6-phosphate dehydrogenase was injected by either electrophoresis or siphoning and mixed with the reagents in the capillary by electrophoretic mixing. Enzyme activity was assayed by electrophoresing the product, reduced nicotinamide adenine dinucleotide phosphate, to the detector where it was detected at 340 nm. Under constant potential, the transport velocity of enzyme and the product was generally different. This caused product to be separated from the enzyme after it was formed. Because product formation was much faster than the rate of enzyme-product separation, product accumulated. The amount of accumulated product was inversely related to operating potential. In the extreme case, the operating potential was zero. Zero potential assays were generally carried out by electrophoresing the enzyme partially through the capillary and then switching to zero potential. This capillary was left at zero potential for several minutes to allow additional product to accumulate. After this additional amplification step, potential was again applied and the product transported to the detector. Product formed under constant potential appears as a broad peak with a flat plateau. When the voltage is switched to zero at intermediate migration distance, a peak will be observed on top of this plateau. Either the eight of the plateau or the area of the peak may be used to determine enzyme concentration. The lower limit of detection was 4.6.10(-17) mol of glucose-6-phosphate dehydrogenase.

Kinetic chromatographic sequential addition immunoassays using protein A affinity chromatography

A new type of chromatographic immunoassay based on sequential addition is described. On a protein A column, the antibody, the sample containing the antigen, and then a known amount of antigen are sequentially injected. This assay is designed to shorten analysis times and reduce complexity of dual-column chromatographic immunoassays, circumvent desorption buffer interferences common to affinity chromatography, and eliminate the need for tagged molecules. This new technique is named kinetic immunochromatography sequential addition (KICQA). Because of its kinetic nature, flow rate will have a large effect on KICQA, and the impact of changing flow rate is studied extensively. By use of various amounts of antibody, the dynamic range of KICQA is shown to be selectable over 2.5 orders of magnitude. Finally, KICQA was used to determine transferrin and albumin in human serum. Both analytes show good agreement with their respective reference methods, and an albumin assay was performed in under 1 min.

Automated real-time immunoassay of biomolecules

ImmunoDetection is a novel technique combining perfusion chromatography technology with antibodies to perform the steps of an immunoassay in a flow-through column format. Sensitive and precise measurements are performed in seconds to minutes using automated liquid chromatography instrumentation.

Process monitoring by parallel column gradient elution chromatography

A system was developed that generates two gradients simultaneously, 180 degrees out of phase. Essential elements of the system were a pump delivering solvent A at a constant velocity, a pump delivering solvent B at a constant velocity, two mixing chambers, and a ten-port valve. By use of this gradient device and two reversed-phase columns packed with 1000-A pore diameter, 8-microns particle size macroporous poly-(styrene-divinylbenzene) resin, six proteins were separated in 40 s in a single gradient cycle.

Capillary electrophoretic separations of proteins using nonionic surfactant coatings

Capillary zone electrophoretic separations of proteins have been achieved by using nonionic surfactant coated capillaries. Capillaries were prepared by derivatization of the silica surface with octadecylsilane followed by the deposition of a layer of nonionic surfactant from an aqueous solution above the critical micelle concentration. This coating is of sufficient thickness and hydrophilicity to reduce both protein adsorption and electroosmotic pumping. This hydrophilic coating reduces electroosmotic pumping 5-8-fold while resolving proteins quickly and efficiently with good recovery. The coating provides a stable and reproducible means of deactivation, while the rate of electroosmotic pumping stays relatively constant throughout the pH range 4-11. This allows the pH to be varied to enhance selectivity without adversely affecting the flow rate.

Coated hydrophilic polystyrene-based packing materials

A very hydrophilic high-performance liquid chromatographic base support was created from microparticulate, macroporous poly(styrene-divinylbenzene) beads. An organic monomer containing cross-linking functionalities was coated on the poly(styrene-divinylbenzene), followed by a catalyzed cross-linking reaction. The coatings formed contain only stable chemical bonds (e.g., C-C, C-O-C), and easily-derivatized hydroxyl moieties. This coated base support was evaluated for hydrophilicity, chemical stability, solvent compatibility, rigidity, and irreversible adsorption. Derivatives of the coated base support were made and applied in various modes of chromatography.

Semipermeable-surface reversed-phase media for high-performance liquid chromatography

Polyoxyethylene was both adsorbed hydrophobically (through the use of non-ionic surfactants) and covalently bonded to reversed-phase high-performance liquid chromatographic packings, thereby establishing a semipermeable hydrophilic layer over the alkylsilane surface. This layer restricts proteins from adsorbing to the alkylsilane phase while permitting penetration and chromatographic separation of small molecules. Biological fluids containing low-molecular-weight analytes may be injected directly, without sample pretreatment or the use of micellar eluents. In the case of adsorbed coatings, surfactant loading was determined primarily by the surface area (over the reversed phase) occupied by the polyoxyethylene head group. Semipermeability of the hydrophilic layer was demonstrated by observing changes in retention of both small molecules and proteins with increasing eluent ionic strength. Coated column stability was evaluated with regard to cumulative eluent volume and repeated serum injections.