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Biomedical subjects

Y H Chu

Publications and source records attributed to Y H Chu.

At least 19 recordsLinked to original sources
PubMed2006

Electrical control of antiferromagnetic domains in multiferroic BiFeO3 films at room temperature.

Multiferroic materials, which offer the possibility of manipulating the magnetic state by an electric field or vice versa, are of great current interest. In this work, we demonstrate the first observation of electrical control of antiferromagnetic domain structure in a single-phase multiferroic material at room temperature. High-resolution images of both antiferromagnetic and ferroelectric domain structures of (001)-oriented multiferroic BiFeO3 films revealed a clear domain correlation, indicating a strong coupling between the two types of order. The ferroelectric structure was measured using piezo force microscopy, whereas X-ray photoemission electron microscopy as well as its temperature dependence was used to detect the antiferromagnetic configuration. Antiferromagnetic domain switching induced by ferroelectric polarization switching was observed, in agreement with theoretical predictions.

Journal Article↗
PubMed2000

Medial cortex strain distribution during noncemented total hip arthroplasty.

Intraoperative proximal femur fractures are a significant concern during noncemented total hip arthroplasty. The current study was performed to investigate the hypothesis that broaching the femur and inserting the stem without using mallet applied impact loads will reduce the risk of intraoperative fracture. Rosette strain gauges were applied to the medial and anteromedial cortex of six human anatomic specimen femurs to compare the strain distribution for broaching and stem insertion. Eight additional femurs were used to compare the strain distribution for stem insertion using impact loading and constant rate stem insertion. For the impact loading stem insertions, the soft tissues surrounding the femur were modeled. Constant rate stem insertions were performed using a mechanical testing machine. The largest strains measured at the medial and anteromedial sites primarily were aligned with the femur hoop axis. The largest strain magnitude, orientation, and sign (tensile or compressive) varied widely among femurs. The stem insertion strains were significantly larger than the broaching strains (two-way analysis of variance with replication). The impact stem insertion strains were not significantly different from the constant rate stem insertion strains. The results indicate that the femur geometry and material properties have a greater influence on the strain distribution than does the implantation technique.

Analysis of Variance↗
PubMed1999

Electrophoretic methods for studying protein-protein interactions.

Protein-protein interactions are involved in many biological processes ranging from DNA replication, to signal transduction, to metabolism control, to viral assembly. The understanding of those interactions would allow the effective design of new drugs and further manipulation of those interactions. Several useful analytical methods are available for the study of protein-protein binding, and among them, electrophoresis is commonly used. We describe two types of electrophoresis: gel electrophoresis and capillary electrophoresis. Gel electrophoresis is a well-established method used to study protein-protein interactions and includes overlay gel electrophoresis, charge shift method, band shift assay, countermigration electrophoresis, affinophoresis, affinity electrophoresis, rocket immunoelectrophoresis, and crossed immunoelectrophoresis. These techniques are briefly described along with their advantages and limitations. Capillary electrophoresis, on the other hand, is a relatively new method and affinity capillary electrophoresis has demonstrated its value in the measurement of binding constants, the estimation of kinetic rate constants, and the determination of stoichiometry of biomolecular interactions. It offers short analysis time, requires minute amounts of protein samples, usually involves no radiolabeled compounds, and, most importantly, is carried out in solution. We summarize the principles of affinity capillary electrophoresis for studying protein-protein interactions along with current limitations and describe in depth its application to the determination of stoichiometries of tight and weak binding protein-protein interactions. The protocol presented in the experimental section details the use of affinity capillary electrophoresis for the determination of stoichiometry of protein complexes.

Animals↗
PubMed1998

Tight-binding streptavidin ligands from a cyclic peptide library.

During the screening of a soluble library of cyclo(AXXXXXAE)K-CONH2, a cyclic peptide cyclo(AHPQFPAE)K-CONH2 was identified as a tight-binding ligand (IC50 = 128 nM) and found to bind 1000-fold more tightly than its linear peptide to streptavidin. The results of this study suggest that library screening of conformationally constrained cyclic peptides can be an effective means for the discovery of high affinity ligands.

Amino Acid Sequence↗
PubMed1998

Simultaneous measurement of nineteen binding constants of peptides to vancomycin using affinity capillary electrophoresis-mass spectrometry.

On-line affinity capillary electrophoresis-electrospray ionization-mass spectrometry (ACE-MS) was used for the simultaneous measurement of multiple binding constants of an all-D-tetrapeptide library to the model receptor, vancomycin. Determination of Kd values for the 19 peptides of the form Fmoc-DXYA is demonstrated. The data are compared with the results obtained for individual compounds using ACE-UV, and good correlation between the two detection methods is shown. Simultaneous determination of multiple Kd values by ACE-MS is achieved in one set of experiments, whereas only one Kd value can be obtained by ACE-UV during the same time. ACE-MS measures multiple binding constants in solution in a fast and reliable manner using femtomole amounts of samples.

Binding, Competitive↗
PubMed1998

Affinity capillary electrophoresis in biomolecular recognition.

Affinity capillary electrophoresis is a new method for studies of biomolecular recognition. Applications reported in the literature include chiral separation of racemic biomolecules, measurement of binding constants, estimation of kinetic on- and off-rate constants, determination of binding stoichiometries (a useful tool in examining electrostatic interactions), estimation of effective charges and molecular weights of proteins, characterization of enzymatic activities and library screening for tight-binding drug candidates in solution. This technique demands only small amounts of sample (nanolitre injection volumes, picograms of proteins), involves no radiolabelled materials or chemically immobilized ligands, and does not require changes in spectroscopic characteristics upon binding. This paper reviews the most recent applications of affinity capillary electrophoresis and its use in the analysis of biomolecules.

Electrophoresis, Capillary↗
PubMed1998

Combinatorial search for diagnostic agents: Lyme antibody H9724 as an example.

Two peptide libraries, Ac-MXXXXXBBRM and Ac-VXXXXXBBRM, were constructed on TentaGel solid support to search for ligands that bind tightly with the H9724 Lyme antibody. By using an on-bead ELISA, approximately 120 ligands were selected as candidates for further study. Matrix-assisted laser desorption ionization mass spectrometry analysis of the candidate ligands indicated a high rate of occurrence of certain amino acids at the randomized positions. On the basis of the initial screening results, a small library was designed and iteratively synthesized. Subsequent library screenings led to the identification of four peptides, Ac-PQEEGX-NH2 (X = R, K, A, D), that showed specific affinity to the antibody. This combination of solid-phase screening and iterative synthesis is an effective strategy for rapid identification of ligands that bind tightly with disease-specific antibodies and should be applicable, at least in principle, to other ligand-receptor systems. This combinatorial library approach can also be a useful tool for the discovery of novel diagnostic agents.

Antibodies↗
PubMed1997

Confirmation of cross-reactivity between Lyme antibody H9724 and human heat shock protein 60 by a combinatorial approach.

A library of Ac-XXXXXPAPRM decapeptides was prepared on a TentaGel solid support using the approach of split synthesis and the strategy of partial chain termination. Epitope screening of the library (17(5) approximately 1.4 x 10(6) decapeptides) with a Lyme monoclonal antibody (H9724) and subsequent MALDI-MS analysis of candidate peptides from colored beads revealed a consensus structure of Xi-DLSXj (Xi = V, L, Y; Xj = G, R). These identified sequences presented no homology to the natural epitope from Borrelia burgdorferi flagellin. However, they were found to resemble a fragment at the N-terminus of human heat shock protein (Hsp60). Our results confirmed that H9724 cross-reacts between bacterial and human proteins and provided support for an autoimmunity mechanism of Lyme disease.

Antibodies, Bacterial↗
PubMed1997

Brachial plexus injury during surgery--report of two cases.

Brachial plexus is the most commonly injured peripheral nerve by malposition during operation. We present two cases of transient brachial palsy after surgery under general anesthesia. Symptoms of the first case persisted about 60 min. Electromyography (EMG) and nerve conduction velocity (NCV) revealed no abnormal finding three days later. In the second case, axonal neuropathy was found at left axillary and suprascapular nerves by EMG and NCV three weeks later. Symptoms persisted for three months and had complete remission after conservative treatment.

Adenocarcinoma↗
PubMed1996

[Effect of norepinephrinergic system on ipalbidine analgesia].

Ipalbidine (Ipa) is a photoactive alkaloid isolated from the seeds of ipomoea hardwickki Hemsl. The analgesic effects of Ipa were determined by rat tail flick method. A dose-dependent analgesic effect was found after s.c. or i.c.v. administration of Ipa, but no analgesia was observed after intrathecal injection, indicating that the analgesic effect of Ipa is central in origin, and it acts mainly on supraspinal substrate. The analgesic effect induced by Ipa (60 mg.kg-1, s.c.) was markedly reduced by reserpine (2 mg.kg-1, i.p.) given 24 h before Ipa, which was reversed by combined administration with i.c.v. norepinephrine (NE). In addition, Ipa-induced analgesia was significantly attenuated by electrolytic lesion of bilateral destruction of locus coeruleus, and combined administration with diethyldithiocarbamate (200 mg.kg-1, i.p.), phentolamine (10 mg.kg-1, i.p. or i.c.v.), and prazosin (3 mg.kg-1, s.c.). But no influence was observed on the analgesia of Ipa after administration of yohimbine (5 mg.kg-1, s.c.) or propranolol (10 mg.kg-1, i.p.). These results suggest that the analgesia caused by Ipa is closely related to the function of the central norepinephrinergic system, and probably mediated by indirectly acting on alpha 1 receptors, but not alpha 2 or beta receptors.

Analgesics, Non-Narcotic↗
PubMed1995

An in vitro bioassay for testing the direct effect of luteinizing hormone-releasing hormone agonists on progesterone secretion by rat ovarian cells.

It is known that luteinizing hormone-releasing hormone (LHRH) and its agonistic analogs could act directly on various extrapituitary target tissues by activating their specific receptors present in these tissues. In this report, we proposed an in vitro assay method for testing the bioactivities of LHRH agonists based on their inhibitory effect on human chorionic gonadotropin (HCG)-induced progesterone secretion by rat ovarian cells. Ovaries from five to ten pseudopregnant rats (prepared by sequential hormone treatment) were mechanically and enzymatically dispersed to prepare luteal cell-rich suspensions. Addition of [D-Ala6, Pro9-Ethylamide]LHRH to ovarian cell suspensions inhibited different concentrations (1, 10 or 100 mIU/ml) of HCG-induced progesterone secretion in concentration-dependent manners. In the presence of 1 mIU/ml HCG as a stimulant, the percent inhibition of progesterone secretion by the same concentrations of [D-Ala6, Pro9-Ethylamide]LHRH was most pronounced and the results were usually more readily reproducible and with less experimental variations. In this study, LHRH and twelve agonistic analogs (at 10(-9) and 10(-7) M concentrations) were compared for their inhibitory effect on 1 mIU/ml HCG-induced progesterone secretion, and their relative agonistic activities were evaluated based on their inhibition potencies. This in vitro bioassay is simple and time- and cost-efficient, and can be employed as a supplementary method to the commonly utilized bioassays for LHRH agonists. This method may also be useful in screening for LHRH agonists with potent extrapituitary effects.

Amino Acid Sequence↗
PubMed1995

Capillary electrophoresis of proteins and nucleic acids.

During the past 30 years, slab gel electrophoresis has been one of the most important tools available to modern biochemistry, biology, and clinical research. However, despite substantial progress in methodology, slab gel techniques typically suffer from laborious, time-consuming and difficult-to-automate procedures. Capillary electrophoresis (CE), first introduced a decade ago, emerges now as an alternative to slab gel techniques with all the advantages of modern automated technology. Although the first target of CE was analysis of small molecules (it is a highly efficient alternative to HPLC), now a main focus is on biopolymers. Currently, CE can be viewed as a fully automated tool for rapid, highly sensitive, and quantitative analysis of minute (nanoliter) amounts of complex samples. This chapter reviews the most important CE techniques and their use for the analysis and characterization of proteins and DNA.

DNA, Single-Stranded↗
PubMed1994

Using affinity capillary electrophoresis to determine binding stoichiometries of protein-ligand interactions.

We have developed a new method utilizing affinity capillary electrophoresis (ACE) for the determination of binding stoichiometries in biochemical systems. Using the same concentration of a ligand in the sample and the electrophoresis buffer, the appearance of an inverted peak corresponding to the free ligand in the resulting electropherogram provides a criterion of binding of a ligand to its receptor protein. For both low (fast off rates) and high (slow off rates) affinity systems, analysis of the integration of free ligand peak in electropherograms as a function of the total concentration of a ligand in samples at constant concentration of receptor protein yields the binding stoichiometry of the ligand to the protein. Applications of this technique to studies of (i) the inhibition of carbonic anhydrases (CA, EC 4.2.1.1, from human and bovine erythrocytes) by 4-alkylbenzenesulfonamide 1, (ii) the interaction of a monoclonal antibody to human serum albumin (anti-HSA) with its antigen HSA, and (iii) the binding of streptavidin (from Streptomyces avidinii) to biotin derivatives (monobiotinylated oligodeoxyribonucleotide 2, fluorescein biotin, or Lucifer Yellow biotin) yield stoichiometries of 1:1, 1:2, and 1:4, respectively. For multivalent, tight-binding systems, this ACE method can readily separate stable intermediate species. This method is generally applicable to both tight- and weak-binding systems, requires only nanograms of proteins and ligands, involves no radioactive materials, and does not require changes in electrophoretic mobilities of receptor proteins upon binding with ligands. It thereby provides a rapid, sensitive, and convenient method for measuring binding stoichiometries of ligands to proteins.

Base Sequence↗
PubMed1994

Determination of binding constants of ligands to proteins by affinity capillary electrophoresis: compensation for electroosmotic flow.

This paper describes the estimation of binding constants (Kb) between carbonic anhydrase B (CAB, EC 4.2.1.1, from bovine erythrocytes) and charged benzenesulfonamides by affinity capillary electrophoresis (ACE) under conditions in which the migration time is affected by changes in electroosmotic flow and by nonspecific interactions accompanying changes in the concentration of ligand. Comparisons of values of migration times of the protein of interest, and of "noninteracting" marker proteins, with those of a neutral internal standard provide the basis for corrections for variable electroosmotic flow; these corrections make possible the estimation of Kb and its uncertainty even in the presence of substantial variations in electroosmotic flow.

Animals↗
PubMed1993

Affinity electrophoresis in multisectional polyacrylamide slab gels is a useful and convenient technique for measuring binding constants of aryl sulfonamides to bovine carbonic anhydrase B.

This paper describes convenient preparations of heterogeneous multisectional polyacrylamide slab gels and the protocols that use these gels to measure protein-ligand binding constants [using bovine carbonic anhydrase B (CAB) as a model system]. Unlike procedures for affinity electrophoresis using tube gels, all binding information concerning protein-ligand interactions was encoded in a single multisectional gel: the procedure involving for measuring binding constants required no postelectrophoresis manipulation of gels. Use of these types of gels improves the accuracy of affinity gel electrophoresis (AGE) by providing reliable internal protein standards. Binding constants measured by AGE agree with those determined in homogeneous solution by spectrophotometric measurements. This technique has been used to investigate the influence of the length of the spacer separating the ligand and the polyacrylamide backbone on the binding constants. Dissociation constants obtained using the affinity gels approach the values measured in free solution, when the spacer is sufficiently long (> or = 18 A); affinity ligands having short spacers give high apparent dissociation constants.

Animals↗
PubMed1993

Use of affinity capillary electrophoresis to determine kinetic and equilibrium constants for binding of arylsulfonamides to bovine carbonic anhydrase.

Affinity capillary electrophoresis (ACE) provides a new approach to studying protein-ligand interactions. The basis for ACE is the change in the electrophoretic mobility of the protein when it forms a complex with its ligand. This binding interaction can be quantified directly for charged ligands or indirectly for neutral ligands in competition with a previously characterized charged ligand. Determination of kinetic and equilibrium constants using ACE relies only on the changes in the migration time and shape (but not the area) of the peak due to protein. Simulation of the protein mobility under conditions of ACE suggests that the experimentally obtained electropherograms can be explained in terms of few variables: on and off rates (and thus, binding constant), concentration of the ligand(s), and relative mobilities of the protein and its complex(es).

Animals↗