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Starkey DE, Han A, Bao JJ, Ahn CH, Wehmeyer KR, Prenger MC, Halsall HB, Heineman WR. Fluorogenic assay for beta-glucuronidase using microchip-based capillary electrophoresis. J Chromatogr B Biomed Sci Appl 2001; 762:33-41. [PMID: 11589456 DOI: 10.1016/s0378-4347(01)00313-9] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Microchip capillary electrophoresis (CE) was used with a model enzyme assay to demonstrate its potential application to combinatorial drug screening. Hydrolysis with beta-glucuronidase of the conjugated glucuronide, fluorescein mono-beta-D-glucuronide (FMG), liberated the fluorescent product, fluorescein. FMG and fluorescein were detected by fluorescence, with excitation and emission at 480 and 520 nm, respectively. Microchip CE was used to separate FMG and fluorescein. Fluorescein production was monitored to assess beta-glucuronidase activity. Michaelis-Menten enzyme kinetics analysis yielded the Km value. The results were compared with those from experiments done by conventional CE. The Km value for beta-glucuronidase with FMG is being reported for the first time as 18 microM. The inhibition of beta-glucuronidase by the competitive inhibitor D-saccharic acid-1,4-lactone (SL) was also determined using microchip CE. Reactions were done with various concentrations of inhibitor and constant beta-glucuronidase and FMG concentrations. A dose-response plot was acquired and the IC50 value for SL was determined to be 3 microM.
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Affiliation(s)
- D E Starkey
- Department of Chemistry, University of Cincinnati, OH 45221-0172, USA
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3
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Abstract
A bead based sandwich enzyme immunoassay coupled to electrochemical detection for ovalbumin has been developed. The enzyme label alkaline phosphatase was used to convert the substrate 4-aminophenyl phosphate to electroactive product 4-aminophenol. The detection was done in a microdrop by continuously monitoring the enzyme turnover with a rotating disk electrode. This reduces dilution of the enzyme product, a key to achieving low detection limits. The assay developed has a detection limit of 0.1 ng ml-1. Assay sensitivity in complex matrices such as food and serum was compared.
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Affiliation(s)
- S Purushothama
- Department of Chemistry, University of Cincinnati, P.O. Box 210172, Cincinnati, OH 45221-0172, USA
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4
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Wijayawardhana CA, Wittstock G, Halsall HB, Heineman WR. Spatially addressed deposition and imaging of biochemically active bead microstructures by scanning electrochemical microscopy. Anal Chem 2000; 72:333-8. [PMID: 10658327 DOI: 10.1021/ac990977q] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A new procedure is described to deposit paramagnetic beads on surfaces to form microscopic agglomerates. By using surface-modified beads, microscopic structures with defined biochemical activity are formed. The shape and size of agglomerates were characterized by scanning electron microscopy (SEM), and the biochemical activity was mapped with scanning electrochemical microscopy (SECM). This approach is demonstrated using beads modified with anti-mouse antibodies (Ab). After allowing them to react with a conjugate of mouse IgG and alkaline phosphatase (ALP), the beads were deposited as agglomerates of well-defined size and shape. The biochemical activity was recorded in the generation-collection SECM mode by oxidizing 4-aminophenol formed in the ALP-catalyzed hydrolysis of 4-aminophenyl phosphate at the surface of the beads. The signal height correlated with both the amount of beads present in one agglomerate and the proportion of Ab binding sites saturated with the ALP mouse IgG conjugate. The feedback mode of the SECM was used to image streptavidin-coated beads after reaction with biotinylated glucose oxidase.
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Affiliation(s)
- C A Wijayawardhana
- University of Leipzig, Wilhelm Ostwald Institute of Physical and Theoretical Chemistry, Germany
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5
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Abstract
A multianalyte immunoassay concept based on the geometric separation of different analyte-specific antibodies has been demonstrated. The assay and amperometric detection are done in a cell with two working electrodes controlled at the same potential, and the amperometric signal at each electrode is monitored. The distance between any two adjacent electrodes in this prototype is 2.5 mm, and during the course of amperometric measurement, the product formed at one electrode does not reach the other working electrode within 20 min after the addition of enzyme substrate. Thus, the method relies on the spatial resolution between the different antibodies being such that measurements are taken before cross-interference due to diffusion can occur. Identical enzyme labels (alkaline phosphatase, ALP) and substrates (p-aminophenyl phosphate, PAPP) are used for all analytes. Alkaline phosphatase-conjugated rat anti-mouse IgG was immobilized by passive adsorption. Our studies showed that this concept is feasible and can be applied to the simultaneous measurement of multiple analytes.
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Affiliation(s)
- Y Ding
- Department of Chemistry, University of Cincinnati, OH 45221-0172, USA
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6
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Abstract
A competitive heterogeneous capillary enzyme immunoassay with electrochemical detection has been developed for phenobarbital in serum. The oxidized primary antibody was attached covalently to the modified interior surface of a microcapillary (22 microl). The competition between analyte phenobarbital and alkaline phosphatase labeled phenobarbital for a limited number of antibody binding sites was complete in 1.5 h. The enzymatic product (p-aminophenol) from the catalytic conversion of the substrate (p-aminophenyl phosphate) was detected by amperometric flow injection analysis. The calibration curve for phenobarbital had a detection limit of 30 microg l(-1) (2.8 pmoles or 0.65 ng) and a range of 30-3000 microg l(-1). The assay could be used to determine the phenobarbital serum concentration in a 4 microl clinical serum sample without pretreatment.
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Affiliation(s)
- J Zhang
- Department of Chemistry, University of Cincinnati, OH 45221-0172, USA
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Dage JL, Ackermann BL, Halsall HB. Site localization of sialyl Lewis(x) antigen on alpha1-acid glycoprotein by high performance liquid chromatography-electrospray mass spectrometry. Glycobiology 1998; 8:755-60. [PMID: 9639536 DOI: 10.1093/glycob/8.8.755] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
A simple, fast and sensitive method was developed to verify the presence of the sialyl Lewis(x) antigen on an N-linked glycoprotein. High performance liquid chromatography-electrospray mass spectrometry (HPLC-ESI/MS) was used to identify which of the five N-linked glycosylation sites of human plasma alpha1-acid-glycoprotein (orosomucoid, OMD) contain the sialyl Lewis(x) antigen. OMD was digested with proteolytic enzymes and analyzed by reversed phase chromatography coupled with on-line ESI/MS. A tandem mass spectrometry experiment was designed to detect the presence of the sialyl Lewis(x) antigen based on the observation of an 803 mass to charge ratio ( m/z ) ion produced in the intermediate pressure region of the ESI interface. The ESI/MS signal at m/z 803 is consistent with an oxonium ion for a glycan structure containing NeuAc, Gal, GlcNAc, and Fuc. The identity of the m/z 803 ion was confirmed by ESI/MS/MS analysis of the m/z 803 fragment ion and comparison with a sialyl Lewis(x) standard. The stereochemistry and linkage positions were assigned using previous NMR analysis but could be determined with permethylation analysis if necessary. The analysis of OMD gave a pattern showing signal for the sialyl Lewis(x) antigen coeluting with each of the five N-linked glycopeptides. The ability to monitor sialyl Lewis(x) expression at each of the five sites is of interest in the study of OMD's role in inflammatory diseases.
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Affiliation(s)
- J L Dage
- Department of Chemistry, University of Cincinnati, Cincinnati, OH 45221-0172, USA, Hoechst Marion Roussel Inc., Cincinnati, OH 45215, USA, and Eli Lilly and Company, Indianapolis, IN 46285, USA
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Dage JL, Sun H, Halsall HB. Determination of diethylpyrocarbonate-modified amino acid residues in alpha 1-acid glycoprotein by high-performance liquid chromatography electrospray ionization-mass spectrometry and matrix-assisted laser desorption/ionization time-of-flight-mass spectrometry. Anal Biochem 1998; 257:176-85. [PMID: 9514787 DOI: 10.1006/abio.1997.2552] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The chemical modification reagent diethylpyrocarbonate (DEPC) was used to modify alpha 1-acid glycoprotein (orosomucoid, OMD) under various conditions. The extents of DEPC modification of the histidine and tyrosine residues were followed by UV spectrophotometry. The resulting modified OMD was analyzed using enzyme digestion, reverse-phase HPLC, electrospray ionization-mass spectrometry (ESI/MS), and matrix-assisted laser desorption ionization time-of-flight-mass spectrometry (MALDI-TOF/MS). The inherent problem of instability of DEPC-modified histidine residues was overcome by adjusting the time scale of the postreaction processing of modified OMD. There were observed differences in reactivity of histidine 97 and histidine 100 that were consistent throughout the pH range 6-8. Furthermore, several lysine residues were modified and the amount of modification increased over the pH range 6-8. These experiments show that HPLC-ESI/MS and MALDI-TOF/MS analysis coupled with enzyme digestion provide the necessary information to describe the reaction of DEPC with OMD. In addition, the results provide the carbethoxy-histidine stability and histidine reactivity information of DEPC-modified OMD necessary for the design of experiments to characterize the drug binding properties of OMD.
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Affiliation(s)
- J L Dage
- University of Cincinnati, Ohio 45221, USA
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Sun H, Dage JL, Halsall HB. Separation of human orosomucoid major gene products using immobilized copper affinity chromatography and identification of the metal-interactive residues. Chromatographia 1997. [DOI: 10.1007/bf02490882] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Affiliation(s)
- M A Cousino
- Dept. of Chemistry, University of Cincinnati, OH 45221-0172, USA
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11
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Bauer CG, Eremenko AV, Ehrentreich-Förster E, Bier FF, Makower A, Halsall HB, Heineman WR, Scheller FW. Zeptomole-detecting biosensor for alkaline phosphatase in an electrochemical immunoassay for 2,4-dichlorophenoxyacetic acid. Anal Chem 1996; 68:2453-8. [PMID: 8694255 DOI: 10.1021/ac960218x] [Citation(s) in RCA: 161] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
A bienzyme substrate-recycling biosensor in a flow injection analysis system is described for the sensitive measurement of alkaline phosphatase (ALP) and applied to the fast readout of a competitive immunoassay for the widely used pesticide 2,4-dichlorophenoxyacetic acid (2,4-D). The phenol-indicating biosensor consists of a Clark-type electrode covered by a membrane with coentrapped tyrosinase and quinoprotein glucose dehydrogenase. ALP dephosphorylates phenyl phosphate to phenol (K(m) = 36 microM) outside the flow system. Phenol is oxidized in the sensor membrane by the oxygen-consuming tyrosinase via catechol to o-quinone. The quinone is reconverted to catechol by glucose dehydrogenase. This substrate cycling results in a 350-fold amplified sensor response to phenol. The oxygen consumption of the enzyme couple in the presence of phenol is monitored as a decrease in current. A total of 3.2 fM ALP (320 zmol/ 100 microL) has been detected after a 57.5 min incubation with phenyl phosphate. All involved reagents are stable over the time of measurement. The sensor does not produce any measurable blank signals. The immunoassay detects 0.1 microgram/L 2,4-D, the maximum concentration for pesticides allowed in drinking water by European Community regulations. The applicability of this biosensor for fast immunoassay readout is demonstrated by a 2 min incubation. By comparison, a standard photometric method (p-nitrophenyl phosphate) requires overnight incubation.
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Affiliation(s)
- C G Bauer
- Institute for Biochemistry and Molecular Physiology, University of Potsdam, Berlin-Buch, Germany
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12
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Abstract
Visualization of immobilized antibodies can be achieved with scanning electrochemical microscopy (SECM) by saturation of the antigen binding sites with an alkaline phosphatase-antigen conjugate, which catalyzes hydrolysis of the redox-inactive 4-aminophenyl phosphate to the redox-active 4-aminophenol (PAP). PAP was detected in the collection mode at an amperometric SECM tip. The tip current reflects the density of active binding sites in the immobilized antibody layer. The application of this approach for immunosensing research has been demonstrated with the optimization of a covalent immobilization procedure of antibodies on glass. The special advantages and present limitations of the procedures are discussed.
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Affiliation(s)
- G Wittstock
- Department of Chemistry, University of Cincinnati, Ohio 45221-0172, USA
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Siles BA, Halsall HB, Dorsey JG. Retention and selectivity of flavanones on homopolypeptide-bonded stationary phases in both normal- and reversed-phase liquid chromatography. J Chromatogr A 1995; 704:289-305. [PMID: 7670627 DOI: 10.1016/0021-9673(95)00269-s] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Three linear polymers of repeating amino acid units, or homopolypeptides, have been individually covalently bonded to microparticulate silica and evaluated for liquid chromatographic separations. The retention and selectivity of seven flavanones were investigated on these stationary phases and a structurally similar, commercially available reference stationary phase, Chiraspher. All three of the homopolypeptide stationary phases retain solutes in the normal-phase mode. The aromatic-containing homopolypeptide stationary phases also retain solutes in the reversed-phase mode. Selectivity values for the flavanones were higher in the normal-phase mode; chiral selectivity was observed for the amphiphilic homopolypeptide stationary phase in the reversed-phase mode. The retention mechanism of each stationary phase is suggested based on the chemical nature and conformation of the corresponding homopolypeptide ligand.
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Affiliation(s)
- B A Siles
- Department of Chemistry, University of Cincinnati, OH 45221-0172, USA
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Yao H, Halsall HB, Heineman WR, Jenkins SH. Electrochemical dehydrogenase-based homogeneous assays in whole blood. Clin Chem 1995; 41:591-8. [PMID: 7720252] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
An electrochemical method has been developed for determining NADH in whole blood for dehydrogenase-based assays by flow-injection analysis. NADH generated by dehydrogenase is oxidized by an electron-transfer coupling reagent, 2,6-dichloroindophenol (DCIP). The reduced form of DCIP (DCIPH2) is measured amperometrically by flow-injection analysis. Endogenous interferents were inhibited by p-hydroxymercuribenzoate. Electrode fouling by proteins was not observed under assay conditions. The Emit theophylline enzyme immunoassay and the hexokinase glucose assay were used as models. For the glucose assay, the intraassay CVs were 15% at 0.31 g/L and 3.5% at 1.82 g/L. Recoveries of glucose from whole blood (compared with that for aqueous standards) were 109%, 97.9%, and 101% at 0.050, 2.00, and 5.00 g/L glucose, respectively, and 104%, 101%, and 102% for theophylline at concentrations of 5.0 (low), 16.4 (medium), and 30.2 (high) mg/L, respectively, with corresponding precisions of 12%, 9.5%, and 8.8%. Both assays correlated well with results by reference methods. These studies demonstrate that this method can measure NADH in whole blood without prior separation and that it is potentially applicable to other dehydrogenase-based assays in whole blood.
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Affiliation(s)
- H Yao
- Biomedical Chemistry Research Center, University of Cincinnati, OH 45221-0172, USA
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15
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Abstract
Abstract
An electrochemical method has been developed for determining NADH in whole blood for dehydrogenase-based assays by flow-injection analysis. NADH generated by dehydrogenase is oxidized by an electron-transfer coupling reagent, 2,6-dichloroindophenol (DCIP). The reduced form of DCIP (DCIPH2) is measured amperometrically by flow-injection analysis. Endogenous interferents were inhibited by p-hydroxymercuribenzoate. Electrode fouling by proteins was not observed under assay conditions. The Emit theophylline enzyme immunoassay and the hexokinase glucose assay were used as models. For the glucose assay, the intraassay CVs were 15% at 0.31 g/L and 3.5% at 1.82 g/L. Recoveries of glucose from whole blood (compared with that for aqueous standards) were 109%, 97.9%, and 101% at 0.050, 2.00, and 5.00 g/L glucose, respectively, and 104%, 101%, and 102% for theophylline at concentrations of 5.0 (low), 16.4 (medium), and 30.2 (high) mg/L, respectively, with corresponding precisions of 12%, 9.5%, and 8.8%. Both assays correlated well with results by reference methods. These studies demonstrate that this method can measure NADH in whole blood without prior separation and that it is potentially applicable to other dehydrogenase-based assays in whole blood.
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Affiliation(s)
- H Yao
- Biomedical Chemistry Research Center, University of Cincinnati, OH 45221-0172, USA
| | - H B Halsall
- Biomedical Chemistry Research Center, University of Cincinnati, OH 45221-0172, USA
| | - W R Heineman
- Biomedical Chemistry Research Center, University of Cincinnati, OH 45221-0172, USA
| | - S H Jenkins
- Biomedical Chemistry Research Center, University of Cincinnati, OH 45221-0172, USA
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16
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Abstract
The concept of a simultaneous dual analyte immunoassay based on two different metal ion labels is demonstrated. The model system consists of two proteins, human serum albumin (HSA) and immunoglobulin G (IgG). Bismuth and indium ions have been coupled to these proteins through the bifunctional chelating agent diethylenetriamine-pentaacetic acid (DTPA). A maximum molar labeling ratio of 6:1 and 10:1 was obtained for HSA and IgG, respectively. Following a competitive equilibrium between unlabeled and labeled protein for a limited amount of specific antibody immobilized on polystyrene, the bound metal ion labels were released by acidification and detected by differential pulse anodic stripping voltammetry (ASV). Limits of detection for HSA and IgG are 1.8 and 0.6 microgram/mL, respectively. Application of the dual immunoassay to human serum samples gave results that were comparable to those obtained by nephelometry.
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Affiliation(s)
- F J Hayes
- Department of Chemistry, University of Cincinnati, Ohio 45221-0172
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Yao H, Jenkins SH, Pesce AJ, Halsall HB, Heineman WR. Electrochemical homogeneous enzyme immunoassay of theophylline in hemolyzed, icteric, and lipemic samples. Clin Chem 1993. [DOI: 10.1093/clinchem/39.7.1432] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
Abstract
We demonstrate here an electrochemical homogeneous enzyme immunoassay for theophylline, which can be performed in hemolyzed, lipemic, and icteric samples. The assay used an unmodified Syva EMIT theophylline kit. One of the enzymatic reaction products, NADH, reacted with 2,6-dichloroindophenol (DCIP) to reduce DCIP to DCIPH2, which was detected electrochemically with flow-injection analysis. The inter- and intraassay coefficients of variation of this manual technique were < 9% at theophylline concentrations of 14 to 34 mg/L. The CVs were 9-15% at low concentrations (6.3 mg/L), which is below the therapeutic range. Analytical recoveries were 91-97% for normal serum and 92-111% for hemolyzed, icteric, or lipemic sera. The measured concentrations (y) were compared with those obtained by the fluorescence polarization immunoassay (x); a scatter plot of the results showed a linear relationship of y = 1.00 x - 0.57 mg/L (r = 0.966, Sy/x = 1.51). This alternative way to measure the serum concentration of theophylline overcomes the shortcomings of spectrophotometric methods, by which it is difficult to measure theophylline in severely hemolyzed, icteric, or lipemic sera.
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Affiliation(s)
- H Yao
- Biomedical Chemistry Research Center, University of Cincinnati, OH 45221-0172
| | - S H Jenkins
- Biomedical Chemistry Research Center, University of Cincinnati, OH 45221-0172
| | - A J Pesce
- Biomedical Chemistry Research Center, University of Cincinnati, OH 45221-0172
| | - H B Halsall
- Biomedical Chemistry Research Center, University of Cincinnati, OH 45221-0172
| | - W R Heineman
- Biomedical Chemistry Research Center, University of Cincinnati, OH 45221-0172
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Yao H, Jenkins SH, Pesce AJ, Halsall HB, Heineman WR. Electrochemical homogeneous enzyme immunoassay of theophylline in hemolyzed, icteric, and lipemic samples. Clin Chem 1993; 39:1432-4. [PMID: 8330402] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
We demonstrate here an electrochemical homogeneous enzyme immunoassay for theophylline, which can be performed in hemolyzed, lipemic, and icteric samples. The assay used an unmodified Syva EMIT theophylline kit. One of the enzymatic reaction products, NADH, reacted with 2,6-dichloroindophenol (DCIP) to reduce DCIP to DCIPH2, which was detected electrochemically with flow-injection analysis. The inter- and intraassay coefficients of variation of this manual technique were < 9% at theophylline concentrations of 14 to 34 mg/L. The CVs were 9-15% at low concentrations (6.3 mg/L), which is below the therapeutic range. Analytical recoveries were 91-97% for normal serum and 92-111% for hemolyzed, icteric, or lipemic sera. The measured concentrations (y) were compared with those obtained by the fluorescence polarization immunoassay (x); a scatter plot of the results showed a linear relationship of y = 1.00 x - 0.57 mg/L (r = 0.966, Sy/x = 1.51). This alternative way to measure the serum concentration of theophylline overcomes the shortcomings of spectrophotometric methods, by which it is difficult to measure theophylline in severely hemolyzed, icteric, or lipemic sera.
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Affiliation(s)
- H Yao
- Biomedical Chemistry Research Center, University of Cincinnati, OH 45221-0172
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19
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Niwa O, Xu Y, Halsall HB, Heineman WR. Small-volume voltammetric detection of 4-aminophenol with interdigitated array electrodes and its application to electrochemical enzyme immunoassay. Anal Chem 1993; 65:1559-63. [PMID: 8328672 DOI: 10.1021/ac00059a013] [Citation(s) in RCA: 248] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
A small-volume voltammetric detection of 4-aminophenol (PAP) has been developed using an interdigitated array (IDA) microelectrode cell in order to apply the IDA to electrochemical enzyme immunoassay. The signal of PAP at the IDA was steady state, and its magnitude was amplified compared with that of the usual single electrode due to redox cycling of PAP between the two finger sets of the IDA. A linear relationship between PAP concentration and cathodic limiting current was obtained from 1 to 1000 microM, reproducibly. The minimum sample volume in the measurement was reduced to 800 nL. High sample throughput of less than 1-min detection time per sample was achieved on 2-10-microL PAP samples. This IDA cell was applied to the electrochemical enzyme immunoassay of mouse IgG. Alkaline phosphatase was used as the enzyme label. The mouse IgG concentration was evaluated by detecting the concentration of PAP, which is the product of enzymatic reaction of the substrate, 4-aminophenyl phosphate (PAPP). Anti-mouse IgG was covalently immobilized on the glass surface of the small-volume immunowells by carbodiimide coupling. The assay range was 10-1000 ng/mL using 10-microL sample and 20-microL substrate solutions.
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Affiliation(s)
- O Niwa
- University of Cincinnati, Department of Chemistry, Ohio 45221-0172
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21
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Abstract
Orosomucoid, a member of the lipocalin family, may function in the in vivo transport of lipophilic compounds such as basic and neutral drugs. We describe the identification of 7-chloro-1-methyl-1,5-benzodiazepine-2,4-dione (clobazam) bound to the serum orosomucoid from individuals actively taking this tranquillizer. This suggests not only that other endogenous factors limit access to the benzodiazepine binding site on human serum albumin, but also that the differential binding of benzodiazepines and their metabolites by orosomucoid should be considered in determining therapeutic doses, particularly in the acute phase response.
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Affiliation(s)
- M Treuheit
- Department of Chemistry, University of Cincinnati, Ohio 45221-0172
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22
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Abstract
Orosomucoid (OMD) contains complex bi-, tri- and tetra-antennary glycan chains. Subfractionation of OMD into three molecular variants using concanavalin A lectin chromatography is based on variations in these complex structures. Standard h.p.l.c. profiles have been developed to analyse the percentage and distribution of the glycoforms present at each glycosylation site in OMD and its molecular variants. The ability to quantify the glycoforms present at each site allows us to extend the earlier results of others and resolve the remaining questions concerning the glycan structures of these variants. Most significantly, the proportions of bi-, tri- and tetra-antennary chains differ at each site for the three molecular variants. The most strongly retained variant from concanavalin A is uniquely capable of possessing biantennary chains at all five sites, whereas the unretained variant is completely devoid of biantennary chains. Only glycosylation site II of the five present is 100% biantennary in the retained and weakly retained variants. In addition, the two gene products of OMD were differentially glycosylated. Molecular masses of the glycoforms were verified by matrix-assisted u.v. laser desorption mass spectrometry. On the basis of the site distribution of oligosaccharides in the variants, efforts were made to understand the factors that control the processing of the carbohydrate chains in OMD. The results indicate that the 'site-directed' model of processing offers the most consistent explanation for the structures seen at the individual glycosylation sites of OMD.
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Affiliation(s)
- M J Treuheit
- Department of Chemistry, University of Cincinnati, OH 45221-0172
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Abstract
An electrochemical method based on differential pulse voltammetry is presented for the determination of AZT in whole blood of fasted subjects. A protein-free supernatant of whole blood is prepared using HClO4 precipitation followed by neutralization with phosphate buffer. The AZT is reduced at a hanging mercury drop electrode. The linear dynamic range of standards in buffer is from the detection limit of 4.1 nM to 206.5 microM (1.1 to 55,200 ng/ml). However, in spiked blood samples the linear dynamic range is from 0.029 to 0.29 microM (7.75 to 77.5 ng/ml). The whole blood assay yields a recovery of 92.30 +/- 5.92% compared to the standard solution assay. After a 30-min preparation time, each sample can be analyzed in 10 min by a manual procedure.
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Affiliation(s)
- G C Barone
- Sharon Drive Corporation, Westlake, Ohio 44145
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Tang HT, Halsall HB, Heineman WR. Electrochemical enzyme immunoassay for phenytoin by flow-injection analysis incorporating a redox coupling agent. Clin Chem 1991; 37:245-8. [PMID: 1993333] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Using phenytoin as a model analyte, we demonstrate an electrochemical enzyme immunoassay based on flow-injection analysis and incorporating 2,6-dichloroindophenol (DCIP) as a redox coupling agent. DCIP reacts with NADH to form NAD+ and DCIPH2, the reduced form of the coupling agent. The production of DCIPH2 is monitored at +250 mV vs Ag/AgCl. This low applied potential improves selectivity in the biological matrix, differentiating against components that are oxidizable at the more-positive potentials required for direct electrochemical detection of NADH. The kinetics-based assay also eliminates other common interferences, mainly from ascorbic acid and glutathione. This system does not require precolumns or analytical columns for isolation of the NADH response. Good agreement with a routine clinical laboratory procedure for phenytoin is obtained for clinical samples (r = 0.95), illustrating the feasibility of such an approach.
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Affiliation(s)
- H T Tang
- Department of Chemistry, University of Cincinnati, OH 45221-0172
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Tang HT, Hajizadeh K, Halsall HB, Heineman WR. Flow-injection analysis with electrochemical detection of reduced nicotinamide adenine dinucleotide using 2,6-dichloroindophenol as a redox coupling agent. Anal Biochem 1991; 192:243-50. [PMID: 2048728 DOI: 10.1016/0003-2697(91)90215-f] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The determination of reduced nicotinamide adenine dinucleotide (NADH) by electrochemical oxidation requires a more positive potential than is predicted by the formal reduction potential for the NAD+/NADH couple. This problem is alleviated by use of 2,6-dichloroindophenol (DCIP) as a redox coupling agent for NADH. The electrochemical characteristics of DCIP at the glassy carbon electrode are examined by cyclic voltammetry and hydrodynamic voltammetry. NADH is determined by reaction with DCIP to form NAD+ and DCIPH2. DCIPH2 is then quantitated by flow-injection analysis with electrochemical detection by oxidation at a detector potential of +0.25 V at pH 7. NADH is determined over a linear range of 0.5 to 200 microM and with a detection limit of 0.38 microM. The lower detection potential for DCIPH2 compared to NADH helps to minimize interference from oxidizable components in serum samples.
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Affiliation(s)
- H T Tang
- Department of Chemistry, University of Cincinnati, Ohio 45221-0172
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26
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Thompson RQ, Barone GC, Halsall HB, Heineman WR. Comparison of methods for following alkaline phosphatase catalysis: spectrophotometric versus amperometric detection. Anal Biochem 1991; 192:90-5. [PMID: 2048739 DOI: 10.1016/0003-2697(91)90190-5] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
An amperometric method for alkaline phosphatase is described and compared to the most widely used spectrophotometric method. Catalytic hydrogenation of 4-nitrophenylphosphate (the substrate in the spectrophotometric method) gives 4-aminophenylphosphate (the substrate in the amperometric method). The latter substrate has the formula C6H6NO4PNa2.5H2O and a Mr of 323. The Michaelis constant for 4-aminophenylphosphate in 0.10 M, pH 9.0. Tris buffer is 56 microM, while it is 82 microM for 4-nitrophenyl phosphate. The amperometric method has a detection limit of 7 nM for the product of the enzyme reaction, which is almost 20 times better than the spectrophotometric method. Similarly, with a 15-min reaction at room temperature and in a reaction volume of 1.1 ml, 0.05 microgram/l alkaline phosphatase can be detected by electrochemistry, almost an order of magnitude better than by absorption spectrophotometry. Amperometric detection is ideally suited for small-volume and trace immunoassay.
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Affiliation(s)
- R Q Thompson
- Chemistry Department, Oberlin College, Ohio 44074
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27
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Halsall HB, Heineman WR. Electrochemical immunoassay: an ultrasensitive method. J Int Fed Clin Chem 1990; 2:179-87. [PMID: 10148952] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
Abstract
Hydrodynamic electrochemical techniques such as liquid chromatography and flow injection analysis with electrochemical detection are very effective for the rapid determination of the enzyme-generated product in enzyme immunoassays. The authors have used this detection method in various assay formats using both alkaline phosphatase and glucose-6-phosphate dehydrogenase as labels. Assays for digoxin will be used illustratively. Recently, the authors have used 70 mL microcapillary hematocrit tubes as the immunoassay reaction vessel and alkaline phosphatase as the labeling enzyme. The assay, complete in 30 min, had a detection limit of 5,6 x 10 -20 moles of IgG in serum. The linear range was four orders of magnitude. This low detection limit is due to a combination of the favorable geometry of the reaction vessel and the suppression of nonspecific adsorption by the addition of ion-pairing blocking agents. Even lower detectable amounts should be achievable with smaller reaction vessels. The capability for detecting such small amounts of analyte is potentially useful for the analysis of extremely small samples such as single cells and blood samples from premature infants.
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Affiliation(s)
- H B Halsall
- Dept. of Chemistry, University of Cincinnati, Ohio
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29
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Gil EP, Tang HT, Halsall HB, Heineman WR, Misiego AS. Competitive heterogeneous enzyme immunoassay for theophylline by flow-injection analysis with electrochemical detection of p-aminophenol. Clin Chem 1990; 36:662-5. [PMID: 2138937] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
A competitive enzyme-linked immunoabsorbent assay based on the flow-injection amperometric detection of p-aminophenol has been investigated with use of the materials and general procedure of a commercial kit for the determination of theophylline in human serum. The antibody is immobilized on glass beads, and the enzyme label is alkaline phosphatase (EC 3.1.3.1). The high currents generated during the electrochemical detection allowed a rapid (35 min) and simple determination of theophylline throughout its therapeutic range (10-20 mg/L) and also in the subtherapeutic range (detection limit of about 80 micrograms/L).
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Affiliation(s)
- E P Gil
- Department of Chemistry, University of Cincinnati, OH 45221-0172
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30
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Gil EP, Tang HT, Halsall HB, Heineman WR, Misiego AS. Competitive heterogeneous enzyme immunoassay for theophylline by flow-injection analysis with electrochemical detection of p-aminophenol. Clin Chem 1990. [DOI: 10.1093/clinchem/36.4.662] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Abstract
A competitive enzyme-linked immunoabsorbent assay based on the flow-injection amperometric detection of p-aminophenol has been investigated with use of the materials and general procedure of a commercial kit for the determination of theophylline in human serum. The antibody is immobilized on glass beads, and the enzyme label is alkaline phosphatase (EC 3.1.3.1). The high currents generated during the electrochemical detection allowed a rapid (35 min) and simple determination of theophylline throughout its therapeutic range (10-20 mg/L) and also in the subtherapeutic range (detection limit of about 80 micrograms/L).
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Affiliation(s)
- E P Gil
- Department of Chemistry, University of Cincinnati, OH 45221-0172
| | - H T Tang
- Department of Chemistry, University of Cincinnati, OH 45221-0172
| | - H B Halsall
- Department of Chemistry, University of Cincinnati, OH 45221-0172
| | - W R Heineman
- Department of Chemistry, University of Cincinnati, OH 45221-0172
| | - A S Misiego
- Department of Chemistry, University of Cincinnati, OH 45221-0172
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31
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Abstract
A sandwich electrochemical enzyme immunoassay with flow injection analysis for the model antigen mouse IgG has been developed with alkaline phosphatase as the enzyme label. The enzyme substrate, 4-aminophenyl phosphate and its enzymatic reaction product, 4-aminophenol have been studied by cyclic and hydrodynamic voltammetry. The determination of 4-aminophenol by flow injection analysis with electrochemical detection (FIAEC) has a linear range of 5.0 x 10(-8) to 1.0 x 10(-5) M, a detection limit of 2.4 x 10(-8) M, and a sample throughput of 72 samples/h. The detection limit is set by a background capacitance response, which depends on the ionic strength difference between the sample and the mobile phase. The sandwich immunoassay has been characterized with respect to substrate concentration for the enzymatic reaction, detection limit, dynamic range and sources of error. Mouse IgG can be determined with a detection limit of 0.81 pg ml-1 by a 30-min substrate incubation time and a six orders of magnitude linear dynamic range.
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Affiliation(s)
- Y Xu
- Department of Chemistry, University of Cincinnati, OH 45221-0172
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32
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Wright DS, Friedman ML, Jenkins SH, Heineman WR, Halsall HB. Sequestration electrochemistry: the interaction of chlorpromazine and human orosomucoid. Anal Biochem 1988; 171:290-3. [PMID: 3407925 DOI: 10.1016/0003-2697(88)90488-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
A simple and rapid method is presented for determination of the association constants and stoichiometries describing ligand macromolecule interactions. Based on flow injection analysis and electrochemical detection by amperometry, the only requirements for direct measurements are that the ligand have redox properties and that these properties change upon binding to the macromolecule. Bound ligand may then be measured in the presence of free ligand. Detection limits are of the order of 2 pmol of ligand or less, a level that should provide access to previously unmeasurable systems. For the exemplary system, chlorpromazine and human orosomucoid, K0ass was determined as 0.39 X 10(6) M-1 with 0.76 chlorpromazine binding sites of this affinity per orosomucoid molecule.
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Affiliation(s)
- D S Wright
- Department of Chemistry, University of Cincinnati, Ohio 45221-0172
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33
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Abstract
Electrochemical enzyme immunoassay methodology has been developed to take advantage of the selectivity of antibody reactions, the amplification feature of an enzyme-based assay, and the ease with which small amounts of the enzyme-generated product can be detected electrochemically. A heterogeneous sandwich enzyme immunoassay was used in this work as the model assay. In this type of assay, the antigen is sandwiched between the enzyme conjugate and a primary antibody that is adsorbed to the solid phase. Alkaline phosphatase is a suitable enzyme for electrochemical assays since it catalyzes the conversion of electroinactive phenyl phosphate to electroactive phenol. The product, phenol, is then quantitated by liquid chromatography with electrochemical detection in a thin-layer flow cell with a carbon paste electrode at 0.895 V vs Ag/AgCl. The current produced by the oxidation of phenol is directly proportional to the analyte (antigen) concentration. The problem associated with these types of solid-phase immunoassays is that the adsorption of the primary antibody is desired while the adsorption of other assay proteins is not. The detection limits are generally defined by the ability to control this nonspecific adsorption. The detection limit of a previous electrochemical assay for rabbit IgG was 100 pg/ml and was limited by a large background current observed in the absence of antigen. In the present study, each step of the assay was examined in order to determine the sources of this background current, and it was found that the major contribution was from the nonspecific adsorption of the enzyme conjugate. Using combinations of Tween 20 and bovine serum albumin as blocking agents, the level of nonspecific adsorption was reduced by 96%.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- S H Jenkins
- Department of Chemistry, University of Cincinnati, Ohio 45221-0172
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Heineman WR, Halsall HB, Wehmeyer KR, Doyle MJ, Wright DS, Wang J, Janata J, Dabuo W, Jinghao P, Agrawal OP, Khatkar SP, van Staden JF, Goyal RN, Rajeshwari, Mathur NC, Otto M, Shouzhuo Y, Lihua N. International Symposium on Electroanalysis and Sensors in Biomedical, Environmental and Industrial Sciences. ACTA ACUST UNITED AC 1987. [DOI: 10.1039/ap9872400324] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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35
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Wright DS, Halsall HB, Heineman WR. Digoxin homogeneous enzyme immunoassay using high-performance liquid chromatographic column switching with amperometric detection. Anal Chem 1986; 58:2995-8. [PMID: 3544954 DOI: 10.1021/ac00127a022] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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36
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Krauss E, Polnaszek CF, Scheeler DA, Halsall HB, Eckfeldt JH, Holtzman JL. Interaction between human serum albumin and alpha 1-acid glycoprotein in the binding of lidocaine to purified protein fractions and sera. J Pharmacol Exp Ther 1986; 239:754-9. [PMID: 3795040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The authors have determined the binding parameters for [14C] lidocaine to several preparations of purified human serum alpha 1-acid glycoprotein (AAG) and human serum albumin (HSA). The authors find that the average Kd for the three different purified AAG preparations was 15.2 +/- 0.5 microM, with an average of 0.567 +/- 0.009 binding sites (N) per AAG molecule, when the concentration of AAG was determined by a standard colorimetric protein assay. The number of binding sites per AAG increased to 0.99 +/- 0.06 when the concentration of AAG was determined immunologically. On the other hand, delipidized AAG had a Kd of 28.0 microM, with an N of 1.72 based on the immunological assay. Various preparations of HSA had Kd/N values ranging from 4.3 to 17.3 mM. The number of binding sites per HSA molecule could not be determined because the maximum concentration of lidocaine that can be used is 10 mM, which is only approximately equal to the Kd. The Kd to HSA was so low and the capacity so high that, at therapeutic concentrations, the binding was in the linear range. Solutions containing both purified AAG and HSA had Kd values of 30.2 +/- 1.8 microM, with 2.01 +/- 0.04 binding sites per AAG molecule. With HSA and delipidized AAG, the Kd was 60 microM, with 3.16 sites per delipidized AAG molecule. This increase in the binding parameters appeared to be due to a direct interaction between the two proteins.(ABSTRACT TRUNCATED AT 250 WORDS)
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Abstract
The reaction between plasmin and alpha 2PI (alpha-2-plasmin inhibitor), which constitutes a major regulatory step in fibrinolysis, involves both interactions between the kringle structures of plasmin and a complementary site on the inhibitor, and also between the inhibitor reactive center and the enzyme active site. An attempt was made to distinguish calorimetrically the two functional domains of alpha 2PI. Only one transition was seen, both in the DSC and UV experiments, contrary to the expected two. This transition was unaffected by K4 of plasminogen but was abolished in the presence of anhydrotrypsin. This suggests the major domain structure in alpha 2PI is associated with the reactive center.
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38
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Abstract
Little is known of the relationships that may exist among the three principal functionalities of glycoproteins. Orosomucoids of closely defined N-acetylneuraminic acid content were examined for evidence of influence of N-acetylneuraminic acid content on the physical properties of the glycoprotein. Fluorescence spectroscopy gave no indication of conformational change in the protein core upon desialylation. Small changes in the chromatographic partition coefficient, sigma, and thermal stability, Td, are interpreted to reflect loss of water of hydration and increased glycan stem-protein interaction without a major repositioning of the chains. Ligand-binding measurements indicate no alteration in the hydrophobic binding domain and a possible interaction between chlorpromazine and N-acetylneuraminic acid. All changes seen are progressive and occur through a region where changes in biological activity are not found. It is suggested that the dependence of biological activity on N-acetylneuraminic acid content in orosomucoid reflects, not coupled changes in protein conformation, but a charge-density-related interaction such that, below a contribution of four or five N-acetylneuraminic acid residues, activity is modified.
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39
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Zarlenga DS, Halsall HB, Day RA, Roth AC. A polynucleotide CD probe: interactions with oligomers of a polycationic amine that exhibit positive extrinsic bands at greater than 300 nm. Biopolymers 1986; 25:407-29. [PMID: 3754470 DOI: 10.1002/bip.360250304] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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40
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Abstract
Dexamethasone disodium phosphate was found to inhibit in vitro fibrillogenesis in a buffered collagen solution that otherwise formed in vivo like fibrils. A nonlinear relationship was observed between the steroid salt concentration and the kinetic parameter half transition time. Full fibril inhibition occurred at dexamethasone phosphate concentrations above 15 mM. At lower concentrations, sample buffers that also contained inorganic phosphate were not different from the control in activation energy of 224.3 +/- 29.3 kJ/mol (53.6 +/- 7.0 kcal/mol). The idea is advanced that the soluble steroid salt associates directly to the collagen and prevents the formation of lateral, hydrophobic interactions between adjacent collagen aggregates.
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41
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Wehmeyer KR, Halsall HB, Heineman WR, Volle CP, Chen IW. Competitive heterogeneous enzyme immunoassay for digoxin with electrochemical detection. Anal Chem 1986; 58:135-9. [PMID: 3511768 DOI: 10.1021/ac00292a033] [Citation(s) in RCA: 84] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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42
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Friedman ML, Schlueter KT, Kirley TL, Halsall HB. Fluorescence quenching of human orosomucoid. Accessibility to drugs and small quenching agents. Biochem J 1985; 232:863-7. [PMID: 4091825 PMCID: PMC1152962 DOI: 10.1042/bj2320863] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The fluorescence behaviour of human orosomucoid was investigated. The intrinsic fluorescence was more accessible to acrylamide than to the slightly larger succinimide, indicating limited accessibility to part of the tryptophan population. Although I- showed almost no quenching, that of Cs+ was enhanced, and suggested a region of negative charge proximal to an emitting tryptophan residue. Removal of more than 90% of sialic acid from the glycan chains led to no change in the Cs+, I-, succinimide or acrylamide quenching, indicating that the negatively charged region originates with the protein core. Quenching as a function of pH and temperature supported this view. The binding of chlorpromazine monitored by fluorescence quenching, in the presence and in the absence of the small quenching probes (above), led to a model of its binding domain on orosomucoid that includes two tryptophan residues relatively shielded from the bulk solvent, with the third tryptophan residue being on the periphery of the domain, or affected allotopically and near the negatively charged field.
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44
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Wehmeyer KR, Halsall HB, Heineman WR. Heterogeneous enzyme immunoassay with electrochemical detection: competitive and "sandwich"-type immunoassays. Clin Chem 1985. [DOI: 10.1093/clinchem/31.9.1546] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Abstract
In these competitive and "sandwich"-type heterogeneous enzyme immunoassays, based on liquid chromatography with electrochemical detection, rabbit immunoglobulin G is used as a model compound. Alkaline phosphatase (EC 3.1.3.1), the labeling enzyme, catalyzes conversion of phenyl phosphate to phenol. After separation on an octyldecylsilane column, the enzyme-generated phenol is detected in a thin-layer cell at a carbon-paste working electrode. The detection limit for phenol is 5.0 nmol/L. The electrode response varies linearly with concentration over a range of three orders of magnitude. For the sandwich-type assay procedure the detection limit is 10 ng/L; the linearity ranges over four orders of magnitude. The detection limit of the competitive immunoassay is 5 micrograms/L. The dynamic range spans two orders of magnitude.
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45
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Wehmeyer KR, Halsall HB, Heineman WR. Heterogeneous enzyme immunoassay with electrochemical detection: competitive and "sandwich"-type immunoassays. Clin Chem 1985; 31:1546-9. [PMID: 3896571] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
In these competitive and "sandwich"-type heterogeneous enzyme immunoassays, based on liquid chromatography with electrochemical detection, rabbit immunoglobulin G is used as a model compound. Alkaline phosphatase (EC 3.1.3.1), the labeling enzyme, catalyzes conversion of phenyl phosphate to phenol. After separation on an octyldecylsilane column, the enzyme-generated phenol is detected in a thin-layer cell at a carbon-paste working electrode. The detection limit for phenol is 5.0 nmol/L. The electrode response varies linearly with concentration over a range of three orders of magnitude. For the sandwich-type assay procedure the detection limit is 10 ng/L; the linearity ranges over four orders of magnitude. The detection limit of the competitive immunoassay is 5 micrograms/L. The dynamic range spans two orders of magnitude.
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46
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Abstract
Sodium dodecyl sulphate (SDS) was used to weaken both the electrostatic and the hydrophobic interactions during collagen fibrillogenesis in vitro. The rate and extent of fibril formation as well as fibril morphology were affected by SDS concentration. Both the formation of large fibrils at 0.3 mM-SDS and the complete cessation of fibril formation at 0.5 mM-SDS were considered to be the result of SDS-induced conformational changes in the non-helical telopeptides. A possible mechanism of SDS interaction with the N-terminal and the distal region of the C-terminal telopeptides is offered.
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47
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Abstract
The redox activation of galactose oxidase by various oxidants is characterized by using a unique thin-layer electrochemical cell. Activation is shown to be strictly a redox process and can be rapidly accomplished by using ferricyanide, cobalt terpyridine or tetracyanomonophenanthroline ferrate, and a control electrode to control solution potential. This oxidation is a one-electron process and does not result in modified galactose oxidase which exhibits enhanced activity. On the contrary, this oxidation is required for activity. The solution potential dependence of activity is independent of which of these mediator-titrants is used, the concentration used, and which of various substrates is used in the determination. The substrates used were acetol, dihydroxyacetone, glycerin, 2-propyn-1-ol, allyl alcohol, 2-butyne-1,4-diol, furfuryl alcohol, benzyl alcohol, 4-pyridylcarbinol, galactose, and stachyose. The E1/2 and n values obtained are 0.40 +/- 0.005 V vs. SHE and 0.9 +/- 0.1 electron at pH 7.3. E1/2 is defined as the potential at which half the maximal enzymatic activity is observed and probably reflects the E0' of the enzymic group involved in activation. A model is proposed in which activation occurs during turnover due to the redox buffering (by oxidants) of an enzymic Cu(II)/Cu(I) state which has a higher E0' than in resting galactose oxidase. The pH dependence of E1/2 is 60 mV/pH unit in the pH range 6.0-8.0. The data suggest that the deprotonation of an amino acid residue facilitates the one-electron oxidation (activation) of galactose oxidase.
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48
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Doyle MJ, Halsall HB, Heineman WR. Enzyme-linked immunoadsorbent assay with electrochemical detection for alpha 1-acid glycoprotein. Anal Chem 1984; 56:2355-60. [PMID: 6517326 DOI: 10.1021/ac00277a022] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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49
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Abstract
Crystals of alpha 1-acid glycoprotein have been grown reproducibly from delipidated protein in the presence of chlorpromazine. The crystals are large hexagonal prisms of space group either P622 or P6(2)22 and the unit cell dimensions are a = b = 101 A and C = 201 A. The unit cell is very highly hydrated and is nearly 80% solvent. It contains one molecule of protein per asymmetric unit. The crystals diffract only to low resolution, presumably reflecting the extensive hydration and accompanying disorder.
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50
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Abstract
Circular dichroism was used to examine alterations in the secondary structure of poly(dA-dT) X poly(dA-dT) upon binding polymer X, a polycationic CD probe for aspects of DNA structure. Stable complex formation is evidenced by increasing Tm and the appearance of large extrinsic bands in the greater than 300 nm, region which increase proportionally with r (ratio of polymer charge to DNa phosphate), in the range 0.0 to 0.32. At relatively low values of r (less than .32), CD spectra of the poly(dA-dT) X poly(dA-dT)-polymer X complex show a gradual non-cooperative inversion in the long wavelength portion (275 nm) of the intrinsic band in low salt solutions suggesting structural and conformational flexibility in poly(dA-dT) X poly(dA-dT) and further implicating polymer X as a potential probe for variations in DNA secondary structure. The dinucleotide repeat configuration of poly(dA-dT) X poly(dA-dT) is presumed to play a role in the observed intrinsic CD changes. NMR data support an "alternating B" conformation for the complex.
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